All this assumes lawsuits and lots of them. Holding out means lawsuits, too. And since you're not a lawyer, nor am I, I'm not sure we can speculate on the outcome of those cases. What we can be sure of is that it would take a long time to settle them. Judgments, decisions, appeals. Lather, rinse, repeat.
It's fine to talk about possibilities, but for a threat to work, it has to be realistic. Among other things, it has to take less effort than the original thing you're threatening against. Threatening to run away from home because your mum makes you take out the garbage only makes sense if you believe that your life on the run will be easier than taking out the garbage. Sure, the players could conceivably start their own league, but by all accounts, it sounds like it'd be harder and more costly than simply saying "We'll take the 50-50."