I wonder: if you spare him from death, will Kehtur make second appearance later in game? Anyone can tell me something about it?
It could be logical to see him somewhere later as (for example) another NPC quest giver - just because we spared him and now he will want to help us with some sort of "secret" quest.
I've finished full NF story without finishing "The Interrogation" as it was possible - now its time to wonder about this side-quest

Here is link from GuildWiki about him: http://gw.gamewikis.org/wiki/Kehtur