My thoughts; IF JTB goes no worse than 10-2 and wins a bowl game then he's the starter going into 2015 (assuming he starts for the entire 2014 season). There's no way that Urban disrupts that chemistry or risks losing Barrett via transfer by inserting Braxton back into the starting lineup.
I believe that Braxton may have jumped the gun on saying that he'll be back next year. If his rehab goes well and he graduates in December, he should probably declare for the draft (regardless of draft projections). He's too good of a football player not to make it at the next level and I think he would be risking a lot by coming back considering his injury history at tOSU.