The Theory: Though Sylvester Stallone has suggested that Ivan Drago will appear in the movie to train his son to fight Adonis Creed, what if, in fact, Drago ends up helping train Adonis for his next fight after Rocky dies, as an act of contrition for killing his father?
Why It Can't Be True: Firstly, it'd be a damn shame to kill Rocky off after he started recovering from his health crisis at the end of Creed, and secondly, does it really seem that likely that a hothead like Adonis would be emotionally prepared to forgive the man who killed his dad?
But..What If?: It would certainly be a clever way to subvert the otherwise fairly cliched way the narrative's probably going to go, with Drago and Rocky training their respective younger fighters for a grudge match that Adonis will presumably win.
Plus, wouldn't a message of forgiveness just be way more interesting and unexpected than a simpler settling of the differences through repeated punches to the face?