1. The GOR isn't a deal with the networks, it's a deal with the conference.  Those schools have signed over their broadcast rights to the ACC.  So I can't imagine the remaining ACC schools (Syracuse, Wake, Boston College, NC State etc) not wanting to get the money from selling those games.

ESPN could maaaybe opt out of the TV deal with the conference (depending on how remaining ACC teams felt about that or how the contract was written), but that wouldn't affect the GOR.

2. ESPN has the deal with the ACC.  That means they are paying $240M annually for the rights to ALL ACC teams (including Clemson, Florida St, Miami and North Carolina) as well as the ACC championship game.

I can't see a world where they opt out of paying $240M for all those games in order to pay more to the SEC for the rights to just 4 of those teams.  ESPN is sometimes dumb, but not that dumb.

3. The more teams that leave the ACC, the harder it becomes to peel other teams away.  If 6 teams left, they'd forfeit all their media rights through 2035.  So 12 years at $17M apiece for 6 teams, means they'd be walking away from a combined $1.224B.... that the conference would still get to keep if they stay together.  Going to be really hard to convince the other 8 to walk away from a $153M per team payout.  Sure they'd do that for the B1G or SEC where they can make an extra $40M/yr.  That pays for itself in 4 years.  But they're not doing that to join the Big 12 and get an extra $10M/year.  The payoff on that is much too long.