It’s possible. These clubs will have war gamed the various scenarios within which UEFA and the various leagues might respond. They will have writs, injunctions etc ready in different countries legal formats and languages for each and will have literally armies of top lawyers ready to go into battle.
This has been planned to death in secret for months. Quite impressive in a manipulative and cut throat way. The authorities either go to battle with them but will need to incur the cost for this or they roll over and basically cede the champions league to them as a compromise. Can see the latter happening personally.