They aren't going to present evidence in a Cease and Desist letter or a formal response. I'm not sure what facts there even are in the two letters. It's Bowlsby saying you did something wrong and ESPN saying they didn't. But at this point I'm not sure how any of us can say there is a great case or no case. We just don't know what Bowlsby has.Assuming all the facts in the letter are correct it’s not enough to go to court with.
While I overwhelmingly expect this to get settled, IF it made it to court I certainly wouldn't be surprised if the result was that UT and OU were compelled by ESPN to talk to the SEC, they didn't notify the other teams, so the GoR cash gets paid, and the rest of the members have the ability to then go their own way and dissolve immediately after without recourse by OU and UT. And that's that.
Where it could get messy would be if UT and/or OU were part of negotiations with ESPN on behalf of the Big 12 while there is proof they were in active discussions with the SEC to join without disclosing that to the rest of the Big 12. Then they have every motivation to torpedo those negotiations.