There isn't much to be honest. What makes GoRs tough is they are not overly complicated, and the stuff like sov immunity is worked out in advance. You can't sign if you can't grant, period. So, FSU would have to pitch they were tricked in some way, maybe breach of contract if they thought they were promised something they weren't delivered, but when FSU and Clemson reupped what they wanted was to have an ACCN, which they got. Now, it doesn't make any money, which isn't a surprise to anyone, but they did receive what they asked for.
Now someone could test a GoR, but it is not like they haven't been tested numerous times over the years. They aren't new nor unique to conferences. There are millions of these things dictating how many albums an artist's owes, to how Spiderman can get in the MCU, to what a production company is making for Netflix. Chip and Joanna even have a giant one with Discovery's creation of Magnolia.
In nearly every case, nullifying it is likely not an option. It comes down to a financial transaction...a make whole. For Texas and the Big 12, it was giving Fox a Michigan game to make up for a Red River.
The problem for FSU is, i don't think they have the leverage they think they do. 15% of the value of the ACC isn't like 15% of the value in the Big Ten or SEC. It is closer to Big 12 money than SEC money. So what you have left is one property worth its weight, ND, about four properties worth about $50m (FSU, Clemson, Washington, Oregon) and a mess worth between $25-40.
FSU's buyout I think is 3-4 years in the ACC's contract, so that's where the $120m came from (since its years of revenue it grows the longer the contract goes on as all have an inflationary growth year to year). They'll need to make up the GoR, for 13 more years, which is valued at around $400m. They're not going anywhere. What they're going to push for is unequal post season revenue payout. That's the part that people haven't spent yet and with the networks focused on that, no one will be paying more for the regular season for a while.