I think any mention of ACC schools is simply a red herring. There doesn't seem to be any way out of the Grant of Rights for them.
Contractually, ESPN reserves the right to renegotiate the contract in the event that there is a change to the conference make-up. So it depends on how bad ESPN wants it and what it’s willing to pay.
They could renegotiate the value of the contract contingent on the release of GOR. They could say if you’re willing to allow the release of these schools we will keep the payout per school of the remaining 12 the same. If you’re not, the value of the renegotiated contract would be so low that it would be a financial detriment to the remaining 12 institutions.
Now I know it’s not that simple. A lot of things would have to happen for it to come to that. But it’s an option none the less.