I vote for the PCs turn and they get replaced by NPCs.
The only other alternative would for the PCs to very slowly (but clear degenerately) zombify or fall into some sort of coma. Then there is some sort of rumor about a cure that they PCs are allured to, but it doesn't sound like that is what you want to with it.
The nice thing about these sorts of games is the funniest things become the greatest type of treasure. A fancy weapon and cure potions might not be that good but PCs, Bags of Holding, Endless Decanters, or even potion of invisibility are certainly worth more.