Well, with Guardians coming to Epcot, something happened. Couple ideas:
1) Disney's been testing out Guardians on a small-scale for several years. They're confident enough that Guardians doesn't fall under the contract, even with Infinity War happening soon.
2) There was a renegotiation at some point. We could possibly see a new Marvel attraction at Universal or a Hulk solo movie maybe (apparently Universal has Hulk solo movie rights locked up). Remember, if a large sum of money changed hands, both Disney + Universal would have to tell that to shareholders. Heck, I would think any contract changes would have to be told to shareholders, even if it's vague.
3) Contract negotiations are currently under way. The Guardians announcement was very vague. Disney is trying to bluff. They have an alternate ride concept ready if their bluff fails. Either way, we get something replacing UoE.