I have released Malmortis from his coffin 6+ times. Somehow he is constantly dying before the quest can finish. I have walked ahead of him, walked behind him, dismissed my voidwalker - nothing seems to keep him from dying. I know I am not doing anything to kill him as he is a ‘green’ NPC so therefore nothing I do should be able to kill him. Right now, I cannot complete this quest.
After 8+ attempts, the quest finally completed. It still needs to be fixed as I am sure there are not a lot that would keep trying, over & over, until it finished.