Bardee,
You've got to let him fly sooner or later, or else you'll be policing him until he's 80.
There are no guarantees in the world of addiction and recovery. The only thing I can be sure of in my life and in the life of my RAD is that we each are responsible for our own recovery. RAD could be sober for 20 years, but no one can guarantee me that she'll stay that way.
Ultimately, your son will be the only one responsible for maintaining his sobriety. And, if he's working a program,he will tell you that he can't even tell you what it will be like at two years sober. Remember, this recovery thing is one day at a time.
Hugs and best wishes,
Hangin' In