It's irrelevant whether NK is "ethnically Armenians" or "populated by Armenians" etc. – neither changes the fact that it is internationally recognized Azeri territory and illegally occupied by Armenian forces. One cannot simply ignore or invalidate this just because the Armenians appear more likable.
Objectively, Azerbaijan has the right to reclaim all of its sovereign territory (if necessarily, by force). It does not have the right to attack Armenia proper, of course.
This has nothing to do with likeability, if Armenia is defeated NK is getting ethnically cleansed.
Pure speculation on your part. Just claiming that something terrible may happen is a weak argument compared to national sovereignty/territorial integrity as core principles of international law – and since one can neither prove nor disprove it, it's a pretty pointless one as well.
This is a country where an ax murderer was pardoned and made a national hero by Aliyev because his victim was Armenian, and state sponsored historical falsification has promoted the idea of Yerevan as part of "west Azerbaijan". "Pure speculation" you say, well assuming that the Armenians of NK will live happily ever after under Azerbaijani rule is far, far beyond speculation. Core principles of international law are not inviolable either, seeing as though the "illegal" independence of Kosovo is usually justified on the grounds of preventing ethic cleansing, but sure the borders are infallible expect for the precedent that supposedly is not a precedent.