@Toturi: Yes, that's exactly what the situation is. They are desperately working to preserve the status quo without leaving a plot hook I can write with later. Which is annoying at several levels. One, because imperfect solutions are way more interesting than perfect solutions, and two, the fact that they're treating it like I have them backed into an impossible situation, when rather, it's merely impossible for them to come out smelling roses and dancing with bunnies.
@Roxy: I don't agree with compelling in any form the sorceress to NPC herself. One, I don't think the player would take it well (as discussed in another thread, my ex girlfriend is playing the sorceress, and things are especially tender between us at the moment because she is now dating another one of my players). Two, I would say that compelling someone to NPC themselves is more or less like compelling them to die in most games.
What the sorceress asked me if she could do was arrange some sort of amplifying field, in which her magic would be stronger than normal, and try and lure the vampire and mercenaries into that to fight. It seemed like that should be possible, but I didn't know how to set up the mechanics at all.