Meh, I think they're going to use their time when she is on the material plane. The deal doesn't make much sense if it was just to corrupt V's soul for the afterlife.

Personally, I think they're going to take V over at critical moments throughout the rest of the story.
Once here, next at Kraagor's gate, then at Xykon's uber dungeon.


Regardless though, I like the fiends, they keep the story going. Without the unnecessary conflict that they (and we) love so much, we'd have no comic. They're sort of like refs or the guy that says, "Can we just get back to the game?" when there's an argument.
Their side is literally our side. /not really the topic for it