I think it's utter insanity to suggest that Universal will give up the rights to the Marvel characters -- especially since those rights include every Marvel franchise. There are three separate movie studios that will be constantly trying to push X-Men, Fantastic Four, Spider-Man, and Avengers in theatres. So multiple times every year those IPs will be getting a big push from Hollywood movie studios, and all that marketing benefits Universal at no cost to them. What's far more likely is that they tear down some old attractions to build new Marvel rides. Men In Black could easily be repurposed into a Guardians of the Galaxy attraction. Why offer Terminator 2 3D when you could have Avengers 3D?
Universal isn't going to give up Marvel unless they get a super-massive payday from Disney.