ok first I want to say that if your gonna be so kind to post spoiler alerts, don't immediately contradict yourself by writing the plot right after. the only spoiler in your thread was in the title. with that said however. My moneys on hagiromo coming in
He can't return unless she exhausts her chakra which seems unreal because Naruto said she has more chakra than the Juubi itself… So R.I.P Madara until further notice.
Even if he returned somehow, he won't be the villain anymore. His plan was casting the IT and creating Eternal peace through it, or what's what he thought. He was finished doing what he wanted. There would be no point for him to return as a villain now.