Lev Lafayette
Mongoose
Nota bene: Crossposted from the RuneQuest-rules mailing list. Comments invited here as well, of course 
Issue
There has been a fair bit of Divine Intervention going on in my campaign of late, mainly out of justified desperation as the difficulty level arcs up. But due the rather random nature of DI, the PCs have suffered a great deal with three PCs losing over 18 points of POW each. You can imagine what it is like with three of the PCs now wandering around with almost no chance of casting a Heal I, let alone resisting a Disruption.
It lead me to do some investigations on the various editions of the game and some thoughts on which is perhaps better that the rather extreme randomness that currently exists.
Summary of Various Divine Intervention Procedures
RuneQuest I & II & III
In RuneQuest I a Rune Priest could call for Divine Intervention with a 10% chance per point of permanent POW previous expended and allocated to the spell at the time of casting. Rune Lords call for Divine Intervention by rolling a table instead, losing between 0 and 10 points of POW. It can be used to raise one adventurer from the dead, or teleport a dozen out of trouble. Divine Intervention can only be used to help the caster, not directly harm anyone else as that would put the Gods in direct conflict of what is a proxy war using humans etc. In RuneQuest II the mechanics are largely the same. The main difference, at least from what I can see, is an Initiate could also attempt Divine Intervention once a week by rolling under their POW on d100, losing that many POW points if successful. It is also clarified that Intervention cannot be used to substitute training and experience and that it can be used to enchant iron or Rune metals. Bound by time, it cannot be used to fortell the future or change the past.
In RuneQuest III it is specified that Intervention is restricted to the God's normal abilities (and bound by Time), an Initiate or Priest may roll D100 and attempt roll below their POW. If they succeed the Intervention occurs and they lose a number of POW points equal to their dice roll. It cannot be used against worshippers of the same God. Characteristics can be raised by 1 point, within species and other limits. Gods are unable to help non-worshippers, cannot create new spells etc, as per previous editions.
RuneQuest: AiG
In RuneQuest Adventures in Glorantha, an initiate, acolyte, priest or lord could call for Divine Intervention. The situation has to be desperate. If a roll equal of less than the character's POW is successful, then the Intervention occurs with the character losing a number of points of POW equal to the roll. A Rune lord rolls 1d10 instead. There are no multiple calls; either the God responds the first time or not at all. Divine effects will concur with the powers of the God. As a rule of thumb, an initiate or acolyte gains access to a number of points of divine magic equal to twice the POW expended in the call for divine intervention, or twice the number of points of divine magic he or she knows, whichever is greater. A priest or Rune Lord gains access to a number of points of divine magic equal to thrice the POW expended or thrice the number of points of divine magic he or she knows, whichever is greater. Worshippers can choose to stack such spells to affect any initiates (or higher ranking worshippers) of the god within range with a single casting. For example, a Humakti could use 5 points of divine intervention granted divine magic to cast a Truesword not only upon her sword, but also on the swords of the four other Humakti initiates in her party, all as a single spell. Further if the worshipper is unconscious or dead when he or she calls for divine intervention, he or she can continue to cast spells granted by divine intervention until the points run out. They cannot cast any other spells while unconscious or dead. A dead worshipper may attempt to resurrect themselves (through the use of the Resurrection spell) after they have healed the wounds that caused their death (through the use of Heal, Heal Wound or Heal Body spells). Due to the Great Compromise, gods will not directly attack mortals. Divine intervention cannot be used against worshippers of the same god, for a god will not act against himself or herself. Gods are unlikely to help non-worshippers. Divine intervention cannot transport an individual into an enemy stronghold or temple where the enemy's power is greatest, but it could be used to escape from such a site.
Mongoose RQ
In Mongoose RuneQuest Divine Intervention may be called by Acolytes, Runepriests and Runelords once per month. Roll D100 and attempt to roll below POW; if successful the miracle occurs, but that amount of POW is lost. Some same powers of a Divine Intervention includes with the casting of any cult spell of any magnitude., allowing a cult spell to affect all worshippers within line of sight., bringing a character back from the dead. Divine Intervention cannot be used to directly harm or slay mortal creatures. It can allow any cult spell to be cast with no limit on magic points or magnitude, it can affect any worshipper within the caster's line of sight, and allow for various 'divine effects' (e.g., temporary double STR, change weather etc).
An Alternative
I don't like the randomness; your RuneQuest may vary. Rather, I would prefer that the character sacrifices an amount of POW in advance for the Divine Intervention. This may be done by an Initiate or Priest. If a character loses either status, the POW dedicated remains dedicated. This dedicated POW does not count towards applications for Priesthood or anything like that.
e.g., Red Mouse is an initiate of Zola Fel and sacrifices 5 points of POW to Divine Intervention. These five points cannot count towards the ten necessary to become a Rune Priest. His own bearing and confidence in himself is sublimated towards that of the mighty river whose valleys and brooks his travels around. To him The River is life itself. Over the course of the seasons however he rescues a young shaman, Penliss, from a rather dangerous situation. She recognises his great spirit and teaches him the ways of the spirit world. He becomes a shaman himself, but does not lose the ability to call upon Zola Fel for assistance. The Gods remember their debts.
When the Divine Intervention is called, the God will intervene automatically. The degree of intervention is dependent on the amount of POW allocated at the time of intervention. The God, rather than the character, will decide in what way they will intervene - after all, no character can tell a God, or their God, what to do. The God will usually be intervene the form of casting Rune spells but other effects can be simulated at an equivalent cost as appropriate to the standard restrictions of the game world (e.g., in Glorantha no mind-reading, altering of time etc) and their domain of activity. Typically an initiate, or even former initiate, will receive twice the POW dedicated and a Rune Priest or Rune Lord three times the amount. As usual, the general rule of thumb of a Spirit Magic spell being the equivalent of half a Divine Magic applies. Stacking limits etc, do not apply to Gods.
e.g., Facing the Watchdog of Corflu and a not insubstantial number of Lunars led by the Coders, Red Mouse watches his friend Honest John fall to the ground due to a well-thrown spear; he immediately calls for Zola Fel's assistance and allocates 3 of his 5 Divine Intervention points; his former initiate status of the cult means that the God will dedicate 6 points of Rune magic power to his aid. Zola Fel hears the call but can do nothing to prevents Honest John's spirit from leaving the mundane plane, as he does not have access to this magic. However, seeing the degree of danger he does Summon a an extremely large large Undine (4 point) which is placed under Red Mouse's control, grants Red Mouse and his ally Praxiletes the Spirit Magic spell River Eyes to aid any escape they require (1 point) and provides a Fireshield (1 points).
The alternative system significantly reduces the amount of power and control that PCs have in terms of access to Divine Intervention, however I feel it is closer to the intention (the Gods are limited to the abilities that they can grant to their worshippers, just not in scale). At the same time however it significantly increases the certainty of access to DI. Finally, it has the additional bonus of treating the Divine forces as actually Intervening by letting the GM roleplay their actions.

Issue
There has been a fair bit of Divine Intervention going on in my campaign of late, mainly out of justified desperation as the difficulty level arcs up. But due the rather random nature of DI, the PCs have suffered a great deal with three PCs losing over 18 points of POW each. You can imagine what it is like with three of the PCs now wandering around with almost no chance of casting a Heal I, let alone resisting a Disruption.
It lead me to do some investigations on the various editions of the game and some thoughts on which is perhaps better that the rather extreme randomness that currently exists.
Summary of Various Divine Intervention Procedures
RuneQuest I & II & III
In RuneQuest I a Rune Priest could call for Divine Intervention with a 10% chance per point of permanent POW previous expended and allocated to the spell at the time of casting. Rune Lords call for Divine Intervention by rolling a table instead, losing between 0 and 10 points of POW. It can be used to raise one adventurer from the dead, or teleport a dozen out of trouble. Divine Intervention can only be used to help the caster, not directly harm anyone else as that would put the Gods in direct conflict of what is a proxy war using humans etc. In RuneQuest II the mechanics are largely the same. The main difference, at least from what I can see, is an Initiate could also attempt Divine Intervention once a week by rolling under their POW on d100, losing that many POW points if successful. It is also clarified that Intervention cannot be used to substitute training and experience and that it can be used to enchant iron or Rune metals. Bound by time, it cannot be used to fortell the future or change the past.
In RuneQuest III it is specified that Intervention is restricted to the God's normal abilities (and bound by Time), an Initiate or Priest may roll D100 and attempt roll below their POW. If they succeed the Intervention occurs and they lose a number of POW points equal to their dice roll. It cannot be used against worshippers of the same God. Characteristics can be raised by 1 point, within species and other limits. Gods are unable to help non-worshippers, cannot create new spells etc, as per previous editions.
RuneQuest: AiG
In RuneQuest Adventures in Glorantha, an initiate, acolyte, priest or lord could call for Divine Intervention. The situation has to be desperate. If a roll equal of less than the character's POW is successful, then the Intervention occurs with the character losing a number of points of POW equal to the roll. A Rune lord rolls 1d10 instead. There are no multiple calls; either the God responds the first time or not at all. Divine effects will concur with the powers of the God. As a rule of thumb, an initiate or acolyte gains access to a number of points of divine magic equal to twice the POW expended in the call for divine intervention, or twice the number of points of divine magic he or she knows, whichever is greater. A priest or Rune Lord gains access to a number of points of divine magic equal to thrice the POW expended or thrice the number of points of divine magic he or she knows, whichever is greater. Worshippers can choose to stack such spells to affect any initiates (or higher ranking worshippers) of the god within range with a single casting. For example, a Humakti could use 5 points of divine intervention granted divine magic to cast a Truesword not only upon her sword, but also on the swords of the four other Humakti initiates in her party, all as a single spell. Further if the worshipper is unconscious or dead when he or she calls for divine intervention, he or she can continue to cast spells granted by divine intervention until the points run out. They cannot cast any other spells while unconscious or dead. A dead worshipper may attempt to resurrect themselves (through the use of the Resurrection spell) after they have healed the wounds that caused their death (through the use of Heal, Heal Wound or Heal Body spells). Due to the Great Compromise, gods will not directly attack mortals. Divine intervention cannot be used against worshippers of the same god, for a god will not act against himself or herself. Gods are unlikely to help non-worshippers. Divine intervention cannot transport an individual into an enemy stronghold or temple where the enemy's power is greatest, but it could be used to escape from such a site.
Mongoose RQ
In Mongoose RuneQuest Divine Intervention may be called by Acolytes, Runepriests and Runelords once per month. Roll D100 and attempt to roll below POW; if successful the miracle occurs, but that amount of POW is lost. Some same powers of a Divine Intervention includes with the casting of any cult spell of any magnitude., allowing a cult spell to affect all worshippers within line of sight., bringing a character back from the dead. Divine Intervention cannot be used to directly harm or slay mortal creatures. It can allow any cult spell to be cast with no limit on magic points or magnitude, it can affect any worshipper within the caster's line of sight, and allow for various 'divine effects' (e.g., temporary double STR, change weather etc).
An Alternative
I don't like the randomness; your RuneQuest may vary. Rather, I would prefer that the character sacrifices an amount of POW in advance for the Divine Intervention. This may be done by an Initiate or Priest. If a character loses either status, the POW dedicated remains dedicated. This dedicated POW does not count towards applications for Priesthood or anything like that.
e.g., Red Mouse is an initiate of Zola Fel and sacrifices 5 points of POW to Divine Intervention. These five points cannot count towards the ten necessary to become a Rune Priest. His own bearing and confidence in himself is sublimated towards that of the mighty river whose valleys and brooks his travels around. To him The River is life itself. Over the course of the seasons however he rescues a young shaman, Penliss, from a rather dangerous situation. She recognises his great spirit and teaches him the ways of the spirit world. He becomes a shaman himself, but does not lose the ability to call upon Zola Fel for assistance. The Gods remember their debts.
When the Divine Intervention is called, the God will intervene automatically. The degree of intervention is dependent on the amount of POW allocated at the time of intervention. The God, rather than the character, will decide in what way they will intervene - after all, no character can tell a God, or their God, what to do. The God will usually be intervene the form of casting Rune spells but other effects can be simulated at an equivalent cost as appropriate to the standard restrictions of the game world (e.g., in Glorantha no mind-reading, altering of time etc) and their domain of activity. Typically an initiate, or even former initiate, will receive twice the POW dedicated and a Rune Priest or Rune Lord three times the amount. As usual, the general rule of thumb of a Spirit Magic spell being the equivalent of half a Divine Magic applies. Stacking limits etc, do not apply to Gods.
e.g., Facing the Watchdog of Corflu and a not insubstantial number of Lunars led by the Coders, Red Mouse watches his friend Honest John fall to the ground due to a well-thrown spear; he immediately calls for Zola Fel's assistance and allocates 3 of his 5 Divine Intervention points; his former initiate status of the cult means that the God will dedicate 6 points of Rune magic power to his aid. Zola Fel hears the call but can do nothing to prevents Honest John's spirit from leaving the mundane plane, as he does not have access to this magic. However, seeing the degree of danger he does Summon a an extremely large large Undine (4 point) which is placed under Red Mouse's control, grants Red Mouse and his ally Praxiletes the Spirit Magic spell River Eyes to aid any escape they require (1 point) and provides a Fireshield (1 points).
The alternative system significantly reduces the amount of power and control that PCs have in terms of access to Divine Intervention, however I feel it is closer to the intention (the Gods are limited to the abilities that they can grant to their worshippers, just not in scale). At the same time however it significantly increases the certainty of access to DI. Finally, it has the additional bonus of treating the Divine forces as actually Intervening by letting the GM roleplay their actions.