There is a very very high chance no matter how good the recovery is going that he will not be playing football anywhere next year. If he recovers fully you are still looking at like a year time frame befire he is good to go.Seems like everyone's discounting it but I think Tua returns for his senor year to prove he's healthy like you say.
No reason to go back to Bama to sit a season. Get drafted at least he is getting paid and then he could focus 100% on rehab instead of having to attend classes as well. If can't make it back on the field he can always go back to school.