Mental health counselor here.
The outcomes of treatment for bipolar disorder are unfortunately very variable. It depends on how severe your son’s symptoms are, how well he responds to the medications cocktail he’s being given, what that medication cocktail is, and how well he adheres to it.
The important thing is that your son controls what he can control, which is largely whether or not he takes his meds and how much he engages in therapy. Therapeutic skills involve insight/mindfulness work (i.e. how well your son can recognize his symptoms as they’re happening) and resource use (i.e. does he inform his therapist and/or psychiatrist when he notices he’s be king symptomatic). Mania often feels amazing to people experiencing it, so they’re often motivated against treating it when it occurs, and this is major barrier to treatment.
A big component is whether or not symptoms of psychosis are involved in either the mania or depression. Psychotic symptoms are: 1.) hallucinations (false sensory perceptions, like hearing voices, seeing things, smelling things, etc), 2.) delusions (false beliefs that don’t conform to “normal” societal beliefs, like “I am Jesus” or “God has a mission for me”), and 3.) paranoia (i.e. feeling people around you are hostile to you or are spying on you, etc). These can be experienced in either mood state, but are most often seen in manic states.
I would suggest getting in touch with an organization called NAMI (National Alliance for the Mentally Ill) as they have tons of resources for people struggling with mental illness and family members of mentally ill people.