Nostalrius Begins - Quality wow vanilla realm (1.12)

NPC that is supposed to end quest dies as soon as he respawns,also when i tried to fight him(before he started to die,when he respawns),he regenereted his health to half and keep attacking me,while supposed to become friendly and let me turn in quest.

I found a fix for this as I had the exact same problem..

You have to pull him down from the stairs he stands at and then bring him to 1/4 hp while hes away from where he normally stands . This will make him friendly and unable to "reaggro" from body pull.