Is that timeline destroyed? Just because it is not the one we are currently in does not mean it is destroyed. You have to ask, in the WoW universe, when an event "changes" in a given time line, is that time line broken because it is no longer "true" or does it branch from the time line where it "changed"

We know there are multiple time lines in WoW. It is assumed that there are multiple because of meddling from "adventurers from the future/past" to preserve OUR present. Meaning the one where we ultimately don't inadvertently free the Old Gods (as a previous KYL: TFH stated).

And since Norz is kinda outside all the timelines/in all of them as one, when he dies, there is no other Norz to straighten out the timeline. He. Is. Gone. Therefore, when he sends you to kill himself, he is dead, no questions to ask. Meaning if he created a separate time line to hide in, if he died in any of them, he would be dead. Period.

Irregardless of what time line Norz dies in, he is dead. No alternates. Dead.