I don't know why Universal would do this anyways. Their Spider-Man ride is considered one of the best at Universal (if not one of the better attractions at any park worldwide); why would they want to give that up and have to tear it down? Plus they'd have to retheme everything in the Marvel area, which would be a large expense. It would also allow Disney to start building Marvel properties at WDW, which would probably pull guests away from Universal and to WDW. I don't think IP like Alien and Predator are valuable enough for Universal to make that kind of swap; it just doesn't seem like it would make business sense to me.
Of course, I hope this never happens for selfish reasons -- although I enjoy the MCU, I don't really care about any Marvel rides, and I'm terrified what Disney would do if they had free rein to start shoving Marvel characters into every corner of the parks.