The ACC GOR does not guarantee ANY amount of money. It only combines the rights of all of the schools so that the conference can negotiate those rights to a media company. The David Hale article you linked to discussed why conferences did that. I think he said the Big10 started it. There is no "equal or lesser" value, because there is no guaranteed outcome in the GOR.
We do not even know that there is a unilateral opt-out available to ESPN. I found an article from 2016 where someone from FSU, can't remember if it was the president, AD, or BOT chair, said that there were look-ins on the contract that he thought would be beneficial to FSU and the ACC, and that the first of those look-ins would occur in 2019. That look-in was delayed until 2025. 2019 is the same year that the FSU lawsuit claims the "opt-out" was originally supposed to occur, but was delayed until 2025. I can't say for sure that it doesn't exist, but it seems rather odd to have both an opt-out and a look-in scheduled for the same time, and delayed by the exact same amount. I have seen some Twitter posts and a blog post that claimed that the "opt-out" and the look-in are two separate occurrences and that there is in fact an actual "opt-out". However, those people had zero evidence of anything and were just speaking as if it were true. The only evidence of an actual opt-out is what FSU put in their lawsuit. The same FSU that claimed in 2016 that a look-in was going to be beneficial to FSU. Unless there is hard evidence released that such an opt-out exists, I will not believe it. If it does exist and ESPN drops the ACC in January, then I will believe it. If ESPN or the ACC make an announcement before January that it exists, then I will believe it. FSU's lawsuit and a lot of pontificators are not going to convince me that it is true. I don't know that it doesn't exist, but I think the evidence leads more in that direction. If it does not exist, then I will never know that it did or did not, unless the ESPN contract is made public.
I agree that the language you pointed to is somewhat concerning. However, I have posted about that before in this thread. If ESPN does have an opt-out and drops the ACC, the ESPN Agreement document will still exist. The ESPN Agreement document will still expressly set forth obligations of the conference. I do not think it is as simple as the GOR is legally invalid if ESPN drops the contract, but I think it will be up to lawyers and courts to decide based on exact wording, the law in whatever jurisdiction has jurisdiction, and precedents in that jurisdiction.
I still haven't read Clemson's lawsuit, but if Hale is stating it correctly, that phrase appears to be part of their argument also. If I understand correctly, Clemson's argument is: The ACC is only obligated by the ESPN Agreement to have 15 teams. If Clemson withdraws, but at least 15 teams remain, the ACC can still fulfill their obligations. If Clemson is no longer a "member institution", their rights are not included in the rights necessary to fulfill the ESPN Agreement. : That seems like a lot of mental gymnastics to me, but that is the kind of contract language entwinement that lawyers and courts deal with all of the time. It is also interesting, because the rumors are that Clemson and FSU voted against adding Stanford, Cal, and SMU. Clemson's arguments would be completely invalid if the ACC had not expanded above 15. Clemson, and the rest of the ACC members, have had lawyers going through the GOR for years. It seems like, if they actually believed this argument is strong that they would have been in favor of adding more teams.