I actually find that kind of interesting. In the contract it's labelled as a "marketing agreement" that he gets $6M for passing each of five HR milestones.
I don't think they'll try to redefine "milestone". I think the obvious angle is to say that because of Alex's conduct he's defamed himself and the Yankees so much that the Yankees have lost all marketing opportunities from him passing those milestones. If Rodriguez passing those milestones is no longer marketable then, at fault by his own conduct, he should not benefit from the marketing agreement.