If Texas went indy and BYU remained indy, there are a couple of possibilities that could be interesting.
1) BYU and Texas could make a scheduling agreement for late season games.
2) BYU and Texas could work on bowl agreements together. They could contract with two bowls a year and the bowl with the bigger payout gets first choice of BYU and Texas.
If you get BYU, Texas, and ND in the independent mix maybe you can round up a couple more teams to form a loose football-only conference that has scheduling agreements, a championship game between the two highest ranked teams, and bowl tie-ins.
The big negative to Texas going indy is it weakens the Big 12 significantly if BYU gets an invite.