Scenario 1: BYU wins the CCG and is rewarded with a 1st round BYE

What needs to happen: BYU defeats Houston (87.2%), at least one of ASU (28.5%) or Iowa St (45.8%) lose...and then BYU wins the CCG (assume this is 50/50).  And then the committee bumps BYU over Boise St (possibly due to a Boise St loss, possibly just due to resume). ESPN playoff predictor lists BYU as having 33% chance to get a first round bye if BYU wins the CCG as outlined

Odds: 0.872 * (1 - 0.715 * .542) * 0.50 * 0.33 = 8.81%

Scenario 2: BYU wins the CCG and gets the 5th autobid spot, playing on the road

What needs to happen: BYU defeats Houston (87.2%), at least one of ASU (28.5%) or Iowa St (45.8%) lose...and then BYU wins the CCG (assume this is 50/50).  ESPN playoff predictor lists BYU as having 50% chance to get a first round road game if BYU wins the CCG as outlined

Odds: 0.872 * (1 - 0.715 * .542) * 0.50 * 0.50 = 13.35%

Scenario 3: BYU doesn't make the CCG...but still gets an at-large bid, playing on the road

What needs to happen: BYU defeats Houston (87.2%), both ASU (71.5%) and Iowa St (54.2%) win...and a LOT of chaos happens elsewhere.  ESPN playoff predictor lists BYU as having 10% chance to get a first round road game in this scenario

Odds: 0.872 * 0.715 * .542 * 0.10 = 3.38%

Note that this overall gives BYU (per ESPN's predictive metrics) a 25.54% chance of making the playoff....but there's one more interesting scenario to consider

Scenario 4: The Big 12 champion (whether BYU or someone else) doesn't make the playoff

What needs to happen: There's a lot of different ways this could happen. The most obvious is if ASU, Iowa St, and BYU all lose this weekend, but it's not the only possibility.  Using data from a few days ago (and again with the simplifying assumption of 50/50 CCG for whichever team makes it), here's the odds of each team to win the Conference.  (see https://www.cougarboard.com/board/message.html?id=34307101 and OP in that thread for a breakdown of where these come from)

• • ASU: 35.43%
  • Iowa St 29.00%
  • BYU: 25.66% (note that this has gone up to 26.7% in the past few days... I just don't want to recalculate for every team)
  • Colorado: 7.14%
  • Kansas St: 1.37%
  • Other:  1.4% (Baylor, Texas Tech, West Virginia)

And per ESPN Playoff Predictor, the odds of those teams missing the playoff if they win the conference are

• • ASU: 11%
  • Iowa St: 13%
  • BYU: 17%
  • Colorado: 63% 
  • Kansas St: 63% (not actually listed by ESPN, but I'd assume it's on the same order as Colorado since they have the same record and CFP rank)
  • Other: 100%

Odds: (0.3543*.11) + (.29*.13) + (.2566*.17) + (.0714*.63) + (.0137*.63) + (.0014*1.00) = 17.53%

Final caveat but these are all based on ESPN predicted probabilities, not my own thoughts or analysis