If BYU goes 11-1, unless both K State and SMU have melt downs in November, there's very little chance BYU gets left out.
Looking at the remaining schedules for both K State and SMU, both will most likely finish no worse than 10-2, which would mean both teams are ranked to finish the season. The chances of leaving out an 11-1 team that has 2 wins over teams that won 10 games and finish ranked in the regular season is pretty low.
It could happen, but it would also call into question the legitimacy of the new 12 team playoff.