Hi,
This happened to me in my game last night. Cast Chicken Claw just near death. Attacked... killed him. He is stuck at 0 HP and will talk to no one except Lohse, who he asks for a gift from. Give him a ton of things, and no dialogue at all after the fight or about anything.
See:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=617705#Post617705