This is NOT a joke but hypothetically how would this affect the Marvel Cinematic Universe (home of Tony Stark the Iron Man and many more)
The movie rights to all Marvel IP originally belonged to Marvel Comics.
Marvel Comics sold the movie rights to X-Men/Fantastic Four to Fox, and Spiderman to Sony.
Then Marvel Comics created Marvel Studios, and started making their own movies. But they can't touch X-Men/FF/Spidey, because those characters got sold.
Disney bought Marvel Comics. By extension, they own Marvel Studios.
Kevin Feige (of Marvel Studios) likes Marvel. He wants all of the Marvel IP to be united under Marvel Studios, to the point where he arranged to "borrow" Spidey back from Sony.
Disney bought Fox.
Disney said some things about wanting to keep things separate and let Fox continue to make X-Men movies under Disney's new "Fox" umbrella. But then Dark Phoenix bombed, and Disney said "Yeah, we're gonna let Kevin Feige take over the X-Men and Fantastic Four. Sorry Fox, but there's gonna be some changes."
You can bet your ass that as soon as he was given permission from Daddy Disney, Kevin Feige went over to Fox HQ with some lawyers, dug up the contracts saying that Fox had purchased the X-Men and Fantastic Four, and burned them. The movie rights to X-Men and Fantastic Four should have reverted back to Marvel Comics, which means that they're Kevin Feige's toys to play with.
Same with Star Wars. Fox owned a partial stake in the original Star Wars (aka Episode 4, A New Hope), which is something that Lucasfilm found annoying and bothersome, so you can bet that as soon as Disney bought Fox, Kathleen Kennedy would have been trying to find a way to get into that building to burn that contract. Or writing a new one relinquishing Episode 4 to Lucasfilm, and forcing Fox to sign it. Fox can't not sign it, Disney's orders (assuming Kathleen Kennedy got Disney to back her up on this).
If Fox and Disney are eventually forced into a divorce, then any property damage that Kevin Feige or Kathleen Kennedy did at Fox while Fox was a part of Disney will go without a response. You can't un-burn a contract.