We have very few patients who have decided to stop taking their regular medication following TMS therapy, although we know of patients who have done so. It is entirely possible to stop taking any kind of antidepressants after TMS therapy, but maintenance sessions would essentially be a guarantee.
Maintenance sessions are necessary because stopping the use of antidepressants will result in chemical changes in the brain as it returns to its normal function, and there is no way to guarantee that the patient will not simply return to a depressive state once this change occurs. With maintenance, the patient can continue receiving some form of treatment for their condition without running as big a risk of relapse.
With this in mind, it is often a good idea to continue taking antidepressants after TMS therapy, provided the medication worked somewhat before. This is because you've just completed treatment based on a certain brain structure, so maintaining that structure with the same antidepressants will ensure the best long-term results.