Not sure if this is a Pathfinder rules question or a Golarion specific setting question. This is a question for a Pathfinder adventure set in Golarion, so I really want to conform to the rules of both (though as the GM, I do have the option of making up my own rules, but I'd rather not).
What happens to a devil when it dies? Does it cease to exist altogether, or does its "soul" (is that the correct word when it comes to devils?) go back to the plane that it came from to get a new body? And if it does return to the Hell from whence it came, how long until it can return to Golarion to wreak vengence on the PCs that killed it?
I'm running a Paizo adventure path, and my PCs are in a position to either kill or bargain with a very powerful devil. They're overthinking the decision (they really should just kill it, because they don't need its help nearly as much as they think), and between sessions, they're emailing back and forth about the questions they plan to ask using the spell Divination to determine how they should handle this. So I'm trying to be over-prepared once they decide which Divination questions to finally ask.