Absolutely not going to happen. There is no way whatsoever that Boise St. could lose to the 20th ranked team and not move down a single spot. Will not happen, there will not be two Mountain West teams in the playoff and only 3 SEC teams. The SEC would blow up the whole thing over that sort of stupidity. Even the ESPN pundits had zero hesitation in saying that Boise State is out with a loss.
What that loss would do is make it extremely hard to keep SMU over Alabama as well if they lose. If Boise State at #10 loses (who by the way was ranked over a one loss SMU at one point) then Alabama will move to #10 automatically meaning they now only have one team (Indiana) between them and SMU. This means SMU losing to the #17 team would need to result in only dropping one spot to stay in the playoff.
For reference, Georgia was undefeated and #1 last year and they dropped to #6 after losing the conference championship game. Boise St. should end up around 14 and once that happens a SMU loss would almost certainly also drop them to #11 or lower as well.
I will be cheering for UNLV because it can only help Alabama's chances. The pundits are trying to make up a rule that conference championship losses don't count, but they've always counted, and the media threw one of the biggest college football fits ever when Oklahoma lost a conference championship game and still played in the BCSCG so they can just shut up and sit down because they're stupid and two-faced.