yeah, and my guess is even if you / we kill them all, we will see them again in act 2. well alive.
A narrative expedient where "if we leave him dead he will be saved by someone else and come back to bite us later" would already work better.
The thing is: nothing like this happens. He doesn't disappear setting the foundations for "Ill be back, bitch".
The guy's corpse just stays on the ground for days with absolute no consequence, in spite of the game clearly telling us of the risk involved.