In my current game, I decided to stealth up to him and filch all his stuff before talking to him and taking him back to the temple.
When I did, I surprisingly found that I could even pickpocket his "dead" body from him. The one you're supposed to loot from him if you kill him, and turn in at the temple.
I even tried to talk to the priest after taking him back to the temple, and found that I could turn in the "dead" body and finish the quest a second time, even though he had already been returned alive.
I'm guessing this is a bug from the original game (though I can't confirm it, as I've never tried to do this in non-Tutu BG), and not a problematic one, just rather amusing.
I also don't know if it's fixable. (I guess that depends on whether the engine has some way to specify that an item should not be possible to pickpocket even though it is not equipped)