Again, this is just my opinion, but I don't believe that it matters how many "years" into a sobriety program Gordon has under his belt. From what we are seeing, it is still about staying sober today for him (as it is with most recovering addicts), right now and for now on. It is a difficult adjustment. But, to answer, he should be in rehab the rest of his life.
And as far as I know, most facilities test for drugs. Facilities are also controlled environments where access to drugs is severely restricted (usually).