If the B12 stays at 10, does it save ESPN money to not renew the BYU contract? Yes. But does it increase their value? I don't thinks so or they would not have signed the BYU contract in the first place.

Relative value right now for ESPN is as stated ~$5-$10M. If BYU goes to B12 and ESPN shares rights with Fox AND ESPN would $10M for half the product. The product (BYU + opponents in Prove) would increase, but to make the deal a wash the product has to double in value and I don't see viewership doubling for every single game.