If you cast Aura of Command on other resurrected creatures or scorpion traps (up to 5, depending on the level of the skill), does that bump him off the list of followers?
Hex editing to replace his character data may work (
Reviving dead NPCs); I'd have to get the data where he hadn't been resurrected from a save after that point in my playthrough. It is probably possible to edit his hit points, as well, but he would need to take some kind of damage for that to kill him.
Zip your latest save and email it to support@larian.com (or reply/PM/email with a Dropbox or Google drive link, etc) and I can take a look at it.
