I agree ESPN isn't the only player. But Fox & ESPN have exclusive negotiating rights window- I haven't seen what that period is. I would be surprised if Fox or ESPN wow the Pac12 with their offers. So they will go out to bid to the Amazons, Apples, NBC, CBS, etc. At that point, we could see them drive a Pac12/Big12 combination or merger.
I am not sure the Big12 wants to end it's deal earlier. And I doubt FOX & ESPN would want to either at this point. That's why the Big12 added 4 teams last summer, to keep the current agreement with ESPN/FOX in place through the 2024/25 FY.
Up to this point, I haven't seen a contract end early. Have you? Even with all the fanfare about the OU, UT, UCLA & USC movement. At this point, the Pac12 schools are the soonest to move in Fall 2024. So the existing Pac12 will remain through 2023/24 sport calendar.
The Big 12/Bowlsby tried working with ESPN last year to start a new TV contract early but ESPN wouldn't negotiate it. Right after that the whole OU/Texas announcement came out... These TV deals almost always get renegotiated a year or two out...