That all makes sense to me. At a certain point you have to ask yourself if the required time that needs to be invested is worth the desired result. Doesn't sound like it in this case.

That seems very strange.

Strange as it may be, it flat out refused to work. AI is notorious for this sort of thing. I'd rather err on the side of consistent results than rely on the possibility that it might work, or might not, depending on how many goats get sacrificed.

Would it be possible, once he reaches Fort Ash, to have him made inactive, removing him from the game, and "replaced" by an already dead version?

Less elegant than a scripted death, but that certainly should be possible. Similar things happen all the time in quests.

Nope, that's not really practical either. I'll just have the corpse enable itself as usual in this circumstance. It's far less hassle than the edge case of you actually being somewhere near the live version of the same NPC.