Do you realize how childish this sounds? For starters if Disney said "deals off" they would have to pay an extremely large sum of money to both Cameron and Fox for backing out of the contract. In addition they would have to deal with the fallout from press/wall street/customers why they announced a major new addition for Walt Disney World that was going to drive attendance and then cancel it a year later which would be made even more difficult if Cameron opened his mouth to the press on why the project fell through.
Secondly, it's not "Disney's way or the highway" if Disney really did want to get out of their parternship, Cameron could EASILY walk over to Universal to make a deal with them, team up with Fox for their rumored theme park project, or even build his own Pandora Park if he wanted to. Cameron is not someone who is going to get intimidated. This is a guy who screamed in Scwarzeneggers face to get him in line when Arnie was acting like a big shot while filming True Lies. He's no shrinking violet nor will he compromise his vision.
Finally, even if we pretended the paragraph you wrote was true and didn't have major flaws in it Disney would have instantly dropped Avatar once Cameron started arguing over a budget (just like Eisner broke up the Star Tours 2 deal with Lucas when Disney refused to give the budget it needed) especially in the wake of the Star Wars acquisition last year. The fact that they didn't do something like that right away should tell you that they couldn't .