20 years of salary plus hazard pay earning interest sitting in a bank would be quite a bit of money. I think the books mention bonuses, but is vague on how much and for what. As the GM you can basically give them as much money as you want.
I would suggest not continuing the campaign after their return. These characters had their epic adventure, time for a new crew to do different things. I usually end my campaigns by allowing each player to narrate what happens over the rest of their character's life. Sort of like you see at the end of some movies. Let each player decide what their character does with their wealth and prestige and share that with the group.