If Lanier is successful at SMU, I'd love to have him back. He's still young enough to have at least a decade in the tank by the time Barnes retires. Successful to me would be multiple NCAA appearances and above average recruiting and development for SMU. Right now he doesn't have the resume to be considered for here but he should have 4-5+ years or so to prove himself.
When Barnes does retire, we aren't going out and hiring a successful P5 coach. Very few programs have that pull unless one of their alumni happens to be coaching at another school. North Carolina promoted an assistant and went straight to the final four.
Hopefully, down the road, Barnes has a coaching tree established from his time at Tennessee. It seems like we are the worst school in the nation in every sport at having players go into coaching.