Killing Nzoth in a expansion which isn't even revoling around it would make me kind of sad (The main theme for BfA still is the faction war, or not?).
I would really like to see one of our heros stabbing us in the back while the factions are battling each other.
That hero which is probably corrupted by Nzoth makes the way for a the next expansion which will then feature Nzoth.
We really need more buildup for our villans. Everything seems so meaningless if the villan is announced not seen since the expansions final raid and then killed.