Everyone wants to know the answer to these two questions, and the answer to the first one is often determined by the answer to the second one!
These issues are often determined by insurance carriers or managed care companies, and no longer by therapists themselves, as used to be the case. Ideally, when the problem that you bring to therapy is resolved to your satisfaction, then you are done. However, therapy is not like going to your physician, and oft times you may find that the source of your depression, for example, lies somewhere beyond the precipitating issue of which you were already aware.
The issue then becomes whether you can afford therapy on your own. That is, do you have enough of your own hard earned money to look at other (perhaps long past) influences which bear on your current depression, or which are somehow linked to the fact that depression is a recurrent state in you life? If you can't afford therapy on your own, then you may be out of luck. Currently, managed care usually dictates that medication(s) should take the place of long term therapy. Should you decide not to take medication or present yourself for a medication evaluation, then you stand the chance of losing what little mental health coverage you have.
Over the years, some therapists may have seen clients longer than was necessary, but most probably have not. While some argue that with the existence of once unavailable medications there is absolutely no justification for long term therapy, others argue that the reason for the long term therapeutic relationship is just that: to provide a relationship. They contend that if someone had either little or no relationship with their parents, or had a horrific relationship with them, then there is no question about the necessity for a long term reparative relationship.
Others complain that without long term therapy, it is impossible to provide for structural personality change. Some counter with the argument that structural personality change is not possible anyway, and that spending health care dollars attempting to achieve it is a waste.
Clearly, there is ample justification for both long and short term therapy. In the end, it is probable that some people, however few, actually need long term therapy for survival, and that many people could use long term therapy, would like long term therapy, and clearly could benefit from it.
No matter which side of the argument you find yourself on, the fact remains that reimbursement for long-term therapy has gone the way of the dinosaur. Therefore, whether you really need it, merely want it, or some of both, you will have to foot the bill yourself.
What should you do? Discuss it with a therapist, talk to your significant other (if you can), look at your budget, determine your degree of reimbursement, and make your determination. More than likely, we could all use a little therapy off and on throughout our lives, and we'd be much happier as a result. It's a bit of a shame that we don't look upon going to a therapist they way we do going to a physician, that is, with much more acceptance and recognition of the value of regular check-ups and attention.