Thanks for your question. My name is XXXXX XXXXX I have over 10 years of experience working in mental health.
The answer to your question about ongoing support often depends on the individual, how severe their Bipolar Disorder is, and how they respond to treatment. If your son is attending a six week outpatient program, it would be very helpful for him to at least continue to meet with a psychotherapist on a regular basis afterwards in order to make sure the transition back to his job is as smooth as possible. Some people prefer support groups and others do not. It certainly wouldn't hurt for your son to explore that option, since typically any positive influences and supports will only help him to continue to manage his symptoms more effectively.
Once your son starts meeting with a psychotherapist, the duration often depends on how well your son manages at work and in his life. If he struggles with the transition back to work, it would be recommended that he continue with therapy at least until he is at a point where himself and his therapist feel that he could be completely self sufficient. At that point he could start meeting with his therapist less frequently, or start meeting with a support group instead, or even transition off these services so long as he is able to maintain control over his symptoms.
Most likely his therapist will be able to make a much better assessment of what types of ongoing services he will needs once he is near the end of his program and closer to the transition of going back to work. At that point they will have a better idea of how he responds to treatment and what he will need to transition back to work. Then it would be important to monitor that transition and making sure that he is receiving all of the supports necessary to make it as smooth as possible, including therapy, support groups, and anything else they feel would be beneficial. I definitely wish you the best with all of this, and if there's anything else I can do to help please let me know.