Yes, once accepted you usually have 2ish weeks (depends on the school) to give them money to hold your seat. Then on May 15th (I think?) each year you have to choose one school, the other schools that you didn't choose then accept new people on their waitlists to fill the seats of people who were accepted but won't attend.
Simple answer is yes, but it also varies depending on the school. Some schools over accept a lot, and therefore nothing happens if someone decides not to attend, especially early in the application process.
Yes, unless it's more than a couple weeks into a school year. If the year has progressed too far the seat is just gone. However, medical schools most likely anticipate this as people from years before takes leaves of absence or remediate a year.
Some schools offer it to the next person on a ranked waiting list and others offer it to the applicant within a pool who has similar demographics to the one declining the seat.
Yes, unless it's more than a couple weeks into a school year. If the year has progressed too far the seat is just gone. However, medical schools most likely anticipate this as people from years before takes leaves of absence or remediate a year.