Frankly, I'm glad I'm not the guy at the negotiating table.
BYU simply has to lay its cards out and say here's what we can/will do and here's what we can't/won't do. Then, if the Big12 says "no thanks", it is what it is.
As others have said, if BYU is going to be on the outside of the P5 for sticking to its beliefs, I'm okay with that too. I won't like it, but I'm okay with it.