Nice change to the OP - lot's of stuff there. Just MO below...
If Mack beats Baylor Saturday he is co-champ of the Big 12. If that happens and if OU beats OSU, then UT would be in the BCS. If UT wins but OU loses, he would be in the Cotton. At the end of the day if he wins the conference outright, no one will fire him. If he is co-champ I personally doubt that they fire him. If he leaves at that point it would be because he is pissed off or unhappy that UT has been putting out feelers for replacements behind his back.
Your info is consistent with info being put out there in certain Texas circles (even certain Texas websites). Mack is gone. It doesn't matter what happens...champs, co-champs, third place, Fiesta, Cotton, whatever. I could not be more sure of this. If I'm wrong, hey, I'll be the first to admit I was wrong. And I recognize that sometimes, the situation is fluid. So I'll say I'm 99.99% sure.
Assuming he does leave, Texas is going to swing big initially...in the words of an influentual donor, the mantra now is Championships...the best predictor of future success is past success. Big money alums have committed to underwriting the cost of a new coach. Texas is going to make an initial run at Nick Saban or Urban Meyers and throw $7 to 8 million per year at them. Urban had visited UT at least three times after he left Florida with interest in the job if it became available. This was before he took the Ohio State job.
Urban's not coming. If Texas had fired Mack two years ago, I am fairly certain Meyer would be the coach at Texas - you're correct that he had expressed interest informally. But that was at a time where there was no collective willpower to get rid of Mack.
John Harbaugh (Ravens) has also expressed interest through backchannels.
This has been reported - I think it's accurate as well. Pro coaches are waking up and realizing that they can make as much money at big time college programs as the NFL and work about 75% as much.
If they strike out with these guys, then you will see the focus slide to the people on the list below. The two names on that list that have been specifically mentioned by insiders are Mahlzan and Mora Jr. Mahlzan's agent has contacted Texas and asked that if the job comes up to call him. It is basically the same story with Mora Jr. who has some kind of relationship with the new Texas A.D., although Mora Jr. just agreed to new deal with UCLA.
I believe Texas would contact Shaw after the top tier (maybe even after a guy like Harbaugh). Shaw would get the immediate approval of the administration as well considering he's a Stanford guy. Consider where Texas' president came from (hint, Cal Berkley).
On a side note, look for Major Applewhite to possibly make a lateral move to be OC at Florida. He and Muschamp are very tight. Major well respected as a coach and gets a lot of credit for the success of UT this year despite some major injuries on the offensive side of the ball.
God help Muschamp. Major has underwhelmed - but I can see Major spinning it to Will that it was due to Mack's meddling. Will, of all people, would understand and believe it.