I believe this subject came up at UofWash. A current student said he'd been accepted in very late (classes already started even), and that the school had emergency sources for situations just like his. UofWash has an excellent financial aid department.
It's probably different at each school, but I wouldn't be surprised if others had this safety in place as well.
Once they accept you, they will do everything in their power to fund you and pass you. There is a reason medical school students are such a great group to loan money to, a huge percentage of those that enter graduate. If they'll let you do things like retake tests to stay enrolled, they're not going to let finances stop you.
My .02 cents.