Texas isn't giving up the LHN, especially now that the Pac 12 has spurned OU. Without that bit of leverage, Texas has them over a barrel (again). And as long as the LHN is in play in its current form, the Big 12 is going to be an endangered league.
It's going to be interesting to see how it plays out. From where I'm sitting, the Pac-12 didn't as much spurn Oklahoma as they spurned Texas. Oklahoma just got caught up in the flames. You're right, though, about a lack of leverage. One of Oklahoma's demands is a change in the revenue inequality. Will Texas concede?
I'm not convinced that Oklahoma can't use the SEC as a bartering tool with Texas. We all know about the state politics that make Oklahoma/OklaSt a package deal and the SEC clearly doesn't want OklaSt. But I read someone yesterday (Clay Travis maybe?) speculating that the SEC might take Oklahoma and OklaSt if that's what it takes to get to 16 teams. And it might take that if NC State and VaTech aren't interested (and I don't think VaTech is...nor would I be if I were in their position). In that situation, the SEC could grab Oklahoma and OklaSt, and Missouri would then follow since the Big 12 would implode. And that's your 16 teams for the SEC.
That's a very far-fetched scenario, but IF it did play out like that, Texas could very easily be left out to dry since the Pac-12 made it clear in its statement that it will not accept Texas' revenue sharing demands. I think Texas has to be careful in all of this, which might force them to play nice with Oklahoma a little more than they'd like to.