50% chance to win each of their remaining games, but the next 2 especially will be tough outs. TeamRankings gives BYU a 63% chance of beating Kansas, 56% chance of beating Arizona St., and an 83% chance of beating Houston which comes out to about a 30% chance of going undefeated.
At this point, the most "likely" outcome is that BYU drops a game to either Kansas or Arizona St. and finishes the season 11-1. That being said, finishing 10-2 or 9-3 would be very surprising and I would say there's about a 75% chance of BYU finishing 11-1 or better - which puts them in the Big 12 championship game and still in the College Football Playoff race. Can't complain about that.