ouch......"they can always hurt you more"Second hand story: A former Navy helicopter pilot was failing out. He figured he would just go back to his old rank and be a pilot again. However, having resigned from the line, not current in any aircraft and not really in a regular year group, they did not take him back. Meanwhile the Navy wanted their due from him for his time at USUHS. He was put in the medical service corps at O-3 with some years of service, but not his previous amount, to pay back few years. I do not know what the final outcome was, but it wasn't what he expected, that is for sure.
Moral of the story: don't go to USUHS expecting that if you fail you will just go back to what you were doing. Going to USUHS after a significant line career can be a gamble in that you are heavily vested in the retirement and if you don't hack at it medical school you may not get that retirement. Basically, don't fail or resign.