If BYU loses one game in conference could they fail to make the CC game (and thus miss the CFP?)

It could happen. Thanks to the victory over KSU, BYU would step ahead of the purple wildcats because of a tiebreaker. So any scenario where KSU wins out basically assures BYU a spot in the CC game as long as the cougs don’t lose more than one game.

I looked over the schedules of all 1-loss teams in the conference that, if they won out, could end up in the CC game.

Of them all only ASU and Arizona create scenarios where a 1-loss BYU gets kicked to the curb. So if BYU loses to Arizona, there is a scenario where ISU (or Texas Tech) and Arizona play with BYU not invited to the CFP dance either.

If ASU were to win out, there is a scenario where ASU and Colorado (or Texas Tech) could play each other in the CC and BYU again misses the CFP, even with one loss.

Of course none of this matters if BYU goes undefeated, or if they lose 2+ games.

What surprises me is the realization that BYU could lose to Utah and still get in the CC game. But if Utah loses to any one of the three: UCF, ISU, of Colorado, they would miss the CC even if they beat BYU.

So beating the Arizona schools is now slightly more important than beating Utah. I would never have guessed that before the season started!