I had the same problem with Ba'al and Geshniz, and there is no way to kill them. Any kind of spell they or their minions shot at me was insta-kill, and Ba'al always starts with a magic blast right after the dialog ends, with zero opportunity to avoid being hit.
I've sent my savegame to the support team and they fixed the problem. While I really appreciate the attention, it would make me an even happier costumer if they release a patch fixing that issue once and for all. I don't theink that there is any other game stopping bug out there, at least I've played for almost 70 hours and found none.
This is an amazing game that I plan to play again sometime after I finish the main game and the expansion, and I would enjoy it even better knowing that this kind of bug will not hinder my progress anymore.
