If BYU is left on the outside in 2025, there will most likely be 6-8 other former P5 teams that will be left on the outside too. At that point, you join forces with them, take the best of the MWC and AAC (BSU, CSU, Memphis, UCF, USF, UConn) and you form a new conference and fight with everything you have for inclusion into the P5 (or P4 at that point) ranks.
I would guess this is the most likely scenario in which BYU joins a conference in the next 10 years.