Anyone could quit the TRT program. They would more than likely just return to their prior levels. Some are able to do a restart with Clomid and other things which can bring levels back to normal. However, for the hypogonadal male, normal is below the average or treatment would have never been applied.
Bodybuilders do "cycle" and go through post cycle therapy to bring their natural production back. Most all steroids will shut someone down to some degree-the severity differs.
TRT is typically for life as you have been shown to NEED supplemental T for quality of life/ medical purposes.