hmm i actually tried that, but didn't go as far as 6 times. but i damaged him enough so that the demon was separated when i broke the pillars. what's interesting though, before putting the demon down i cast peace of mind on Sebille, and she got the 'demonic possession' status, but none of the effects. the fight was over, the dwarf and the priest were happy, the quest closed, but the effect still lingers and is marked 'permanent'. i wonder if that's just a harmless bug.