Well, I think I know how Disney could pull this off in a rather dirty way without paying Universal...
First of all, let me say that there is no way Universal is getting rid of Marvel. There is too much risk and cost involved for both parties. Downtime of the land for Universal and the risk undertaken when they can sit idly by and improve the surrounding areas and capitalize off the superhero boom.
The way Disney does Universal is already laid out methinks... Disney has updated and rebooted many of the characters present at IOA, even the comic books have been rebooted (there are now gay characters and new backstories, correct?) so now all the characters have new "i) basic story line, (ii) the powers, (iii) basic personality traits, (iv) physical appearance (including clothing or costume)."
Universals characters are no longer abiding by the rules of the contract and are not representative of the characters current situations. This is a violation of contract unless there is some reference of the use of legacy stories, powers, personality traits, etc. Maybe someone who knows the contract better than I can comment on this.