In any given year, more than half of all applicants to allopathic medical schools do not matriculate in that cycle to an allopathic school. Clearly, some go to osteopathic schools, some may go to off-shore schools. You can bet that thousands of science majors apply but don't get admitted to med school.
Granted, I usually see people who reapply.
Some teach high school, tutor or teach test prep classes. Some get jobs in research labs or in quality control labs (e.g. doing microbiology checks of manufactured products). Some work in clinical research at a med school (recruiting subjects, obtaining consent for research, handling regulatory paperwork, collecting samples and data which may include learning how to draw blood, etc).
Some take a job doing something flexible to make it easier to reapply: retail sales and substitute teaching are two that come to mind.