Thanks for the ping.
My guess as to why they disappeared...
Some of their tribe became enamored with certain philosophies and ideologies of a distant tribe. The underlying principles of those philosophies and ideologies was that the Nok did not deserve to live and that the Nok were the source of all evil in the world.
Now, the Nok prided themselves on being reasonable folk and had adopted a rather silly mindset that all opinions were equal in value.
So, the Nok had no ability to defend themselves from this attack that came from among their own and they ended up being “death counseled” into non existence.
:’) Maybe they wound up converted to Islam (or dead if they refused).