There are very few guarantees, which are simple:

1) If you are a P5 conference champion, you get an auto-invite to a NY6 bowl,
2) If you are a member of a P5 conference AND your conference champion was invited to the CFP YOU MIGHT receive an invite to a NY6 bowl IF you are deemed worth, and
3) If you are a member of a G5 conference AND are deemed to be the most worthy of the G5 teams by the CFP committee, you will get an invite to a NY6 bowl.

Where in there is a guarantee that BYU, even an undefeated BYU, gets an invite to a NY6 bowl? Is it more likely if BYU is undefeated? Sure. Maybe. But, there is no guarantee. It's NOT likely if BYU is undefeated.

Where in there is a guarantee that BYU, even an undefeated BYU, gets an invite to the CFP? NOWHERE. Unless there ARE NO undefeated teams AND every P5 champion has 2 losses or more, BYU will never sniff a CFP invite.

Sorry to burst anyone's blue goggled bubble.