OK, a quick review of Mack's contract and thoughts on the threat of litigation and litigation itself.
First, a few caveats:
1) It's Christmas so I only briefly skimmed Mack's contract and extension.
2) I am not licensed in Texas so not familiar with any laws special to Texas or the Travis County jury pool.
3) My area of practice is not contracts or contract litigation but I have drafted and litigated breach of contract cases in the past.
That being said, Mack did not need to resign to be terminated. Resignation and falling on one's sword is just the time honored way of terminating a relationship which saves face and honor to the terminated employee who is under performing. The contract clearly states that the AD will review Mack's performance and may choose to terminate at any time. If termination occurs, UT's obligations end on the date of termination and the applicable buyout payment is then due.
So terminating Brown does not form the basis of any legal action itself. Brown and his team (not sure if Jamail is included in this, he may be but he may be conflicted out--always smelled rotten that one of the biggest boosters was the attorney for the HC) though are looking at whether UT acted in bad faith by trying to prospectively terminate the contract and discuss his replacement while the contract was in place ( the replacement could be Saban or me, doesn't matter).
From a legal perspective, I don't see a solid basis for a suit. mack could have been fired last year just as easily as this year. From what we have heard, Powers elected not to fire Mack (not his call, power is with the AD) if he met certain conditions. This agreement was most likely oral and a gentleman's agreement, hence why Mack thought he could fudge it.
The initial outreach for feeling out any options post-Mack supposedly started with a regent not acting in any official capacity with the university. Private citizens can talk to anyone they want and discuss any options they Want to discuss. He could not bind UT unilaterally even if he wanted to. It should also be obvious that UT officially has reached out to several coaches prior to terminating Mack to at least guage interest. That seems like standard business practice and not a breach of any provision of the contract. No AD decides to terminate their head coach without looking at available options.
So I don't see much chance of success.
That doesn't mean that he won't sue. In America, the beauty and failure of the legal system is open access to the courts even when the chance for success is speculative at best.
Also, as I have stated before filing suit will kill Mack's current "job" and relationship at UT and Texas. It will also most likely kill any hopes of another head coaching job or job with the media because these employers don't like employees that bite the hand that feeds.
So, if true, my take is that it is nothing more than a bluff and saber ratlking. But to what point? What is Mack trying to accomplish? Put his stamp on the next HC? If he had not lost his last ally in Powers by breaking his promise to resign, he did so by sourcing that Forde story. I don't see any way that Mack is not on the outside looking in and remaining so for a long time.