In Batracer it happens, I've seen it in a private game we had with 10-11 players.
In real life, if there is such a situation, I suppose the race would be abandoned. From 20 players if there are less than 8 left, then there's seriously something wrong.
I don't remember exactly, but in Indianapolis, 2 years back, we had only 6 players racing.. I suppose they all got points?