Manic states are often associated with an increased sense of self worth. This is fine if it leads to creativity at work, but a problem if it leads to unrealistic grandiosity. Unfortunately, the more severely manic an individual is, often the more out of touch with reality he or she becomes, to the point where reasoning becomes futile. I suggest that you and the other persons to whom he is most likely to listen confront him bluntly with the consequences his remaining off medication, such as hospitalization, involuntary commitment, loss of job, etc. This is one reason for establishing a solid, trusting relationship with a psychiatrist.
Some psychotherapists still discourage medication, but that is uncommon with bipolar disorder.
It is possible he is hearing what he wants to hear, rather than what the therapist has actually said. One negative long-term consequence is simply the fallout of being ill. One really does risk the loss of job, marriage or fianc e and financial well-being, as well as facing the demoralization that comes from squandering opportunities due to an avoidable illness. Finally, what you're dealing with is very difficult for one person. Use another friend or confidant to aid you in trying to get through to him.