PAC12 and superior to the best from the Big12.
With at least 1 loss, neither the Big12 champ (Baylor) nor the PAC 12 champ (ASU) would likely be in the playoff.
With 2 losses already, it’s pretty unlikely Clemson will be in the playoff. At this point, will the ACC champ make the playoff?
Having proven themselves superior to 2 P5 conferences, a 12-0 BYU would certainly have a solid argument for a spot in the playoff.
In your scenario, I’d give BYU about a 50/50 shot at getting the spot in the playoff. Okay, maybe this is optimistic.
If BYU didn’t get the spot, it would be seen as a gross injustice to not give BYU a spot in an NY6 bowl.
To answer your question, I’d say it would be highly probable that BYU gets at least a spot in an NY6 bowl in the scenario you’ve laid out.