Notre Dame has an exit fee built into the contract, they're actually rather easy.
"The Fighting Irish TV deal with the ACC includes a sizable exit fee,
but Notre Dame would be free of paying the Grant of Rights charge for football, according to
ESPN's David Hale."
...
247sports.com
I'm talking about the other schools. And yes it isn't "nothing" but it's short term revenue that would find them in the same spot a decade from now. The ACC schools might be inclined to take whatever negotiated penalty from an exiting school (who's going to exit anyway).
The ACC schools are only getting something like $36 million per year. If they truly would get the estimated $100 million from the new B10 contract (for instance) they could easily offer up $250million now, paid over X years, which would represent about 1/2 of their TV revenue over the remaining contract. Of which, they'd basically make up in additional revenue from the B10 contract within 5 years.
And technically, teams could just sign on with the B10 -- to start in 2036. They'd be lame ducks in the ACC until then like Texas and OU are now. And once that's announced, attempt to negotiate down.
Again, there's lots of ways around this.