Texas is definitely staying with OU.
I've said for the past ten years that OU actually has the power in the relationship. Texas was fine to stand pat in the B12, because Texas wanted to keep it more regional and not endure the far-flung travel associated with joining any of the other conferences, especially for the olympic sports.
But OU has had wanderlust ever since 2010, I believe they felt they missed out in those two rounds of realignment and haven't been satisfied staying in the B12 ever since.
So I'd agree with the reports you've heard-- OU was going no matter what, and Texas' hand was forced, because we know we need them and the TX-OU rivalry, to maintain our sports brand. Sure, an OOC rivalry could be set up, indeed the TX-OU rivalry existed as an OOC game for 8 decades before it become an in-conference game. But there's risk to that-- it's not the 1920s anymore, and times are quite different. How many rivalries have survived in the past 3 decades, when one or both teams switched to different conferences?
Anyway, if the B1G really wanted Texas, they'd need to be willing to take OU. There are factions at OU that would have preferred the B1G all along, but the B1G wasn't overly receptive, given their academics. If that has changed, then now would be the time for the B1G to make a push for both teams.