In that scenario, the PAC12 falls apart. Utah, Colorado, UCLA and probably one more (Cal maybe?) end up in the Big 12 and the Big 12 is very much strengthened.

But the question was about scenarios where the Big 12 doesn't make it to 2024 with BYU. The scenario I outlined isn't one that I think happens, but it is the only way I see that happening. And it definitely requires the B1G not poach the PAC12 and for the PAC12 to poach the Big 12 (which they are capable of doing, so long as they retain their high-profile programs listed above)