Madara is coming back. Because villains always get final words, and Madara didn't get his. This is shonen people, it's freaking formulaic. Ultimately it's a Japanese manga, meant for Japanese viewers.
I lived in Japan for many years now, I can tell you one thing. Kishimoto and Kubo do not give a *crap* what some American otaku thing about their manga. Especially you lot of freeloaders here on base. Japan is a machine. IT does what Japan wants. Japan is in a real sense akin to living life in the Infinite Tsukuyomi. Things work as if you are in a dream, a model society. But I digress, Japan is not the topic here.
Madara is coming back for 1 more reason. He has unresolved plot. Lest we forget, he needs to tell that Edo Hokage what is up with the final fight. Plus he has some small part of the Sage's power left in his lower body (notice how it hasn't disappeared like the res t of him did?)
Madara said he was immortal. Honestly, I doubt he was bluffing. Check the last panel before he came down to confront BZ (He pretended to confront Sauce/Naruto, but was talking to BZ). He clearly used some jutsu, likely it was his clone that got sealed. I doubt Madara is Final villain, but yeah... He's definitely coming back for a short Madara spin.