At the very bottom of the barrel, without making a single legal argument, Texas could have walked away from the Big 12, just said "sue us", then never ever paid the judgement since the Texas Legislature has to authorize payouts for judgements against state entities. That wouldn't ever actually happen. There was also the option of "contract performance" under which they skipped to the SEC, and told the Big 12 they were free to pocket the revenue for any Big 12 games Texas played in Austin - as per the contract. That would be "none".
In the end, it was easier to play out the deal. It let the SEC prepare their own schedules as well.
FSU is looking at sacrificing over $300million over the course of the contract relative to what they could be earning. I can only assume there's a vaporware understanding with other conferences to take them.