Well, the way it's described in - I think - "Arcane Lore", the ritual to discorporate is just like other HeroQuests with community support modifiers for the shaman on the spirit plane etc. It says a bunch of other strange stuff as well, though, such as that if a shaman discorporates and leaves the ritual circle, his body disappears and (with practice) he can actually leave the Spirit Plane in a different place and re-appear there.