UEFA have no leverage. Whatever they'll say, it's done, and they are helpless. They need top clubs, top clubs don't need them.
Are UEFA threatening to ban clubs from the transfer market? Fine, they'll create their own market. And, by the way, good luck to small clubs with selling their stars, since in this case they'll have to forget about big bucks from RM, MU, Juventus, etc. In other words, UEFA will just make things much worse for the rest of football world, and will be hated for it.
Are UEFA threatening to ban players from the NTs? Clubs will be just happy. Imagine: no NT breaks. No injuries because of them.
What else those corrupt bureaucrats can do? Nothing. All they can really do is to sit and watch billions of dollars leaving their revenue streams.