CapnZapp
Legend
I have the module on pre-order; how do you all have it?
How about applying 10 HP of Necrotic damage each time that reduces the PC's HP maximum that is permanent until the Soulmonger is defeated? (Just like undead.) You could use this as a hook or basis for clues - maybe a PC that has been raised gets a flash of insight from the trapped part of her soul?
Instead of raise dead no longer working, it still works, but the raised character contracts the withering disease all other raised people have contracted?
Bunching these two posts together - it's pretty much the same idea: as I understand it the disease is that you lose one point of maximum hp each day until you reach zero and is vernichted (annihilated).
Yes, since none of the characters have been resurrected (yet) this is probably what I'll do.