O.K., so this car had severe rear end damage, almost undrivable, but, was on the road anyway. The owner never called it in cause it was his/her fault for backing into a tree or something very hard.

A few weeks pass.

Now another car runs into it but, very lightly only producing a couple of hundred dollars worth of damage to itself and very minimal damage (possibly a small dent) to the already severly damamged. Basically, not much of any damage to either car.

How would they determine what the 2nd car did? Would they be liable to fix the whole rear end? I know there really wouldn't be a way to repair a small dent in a crushed rear end (or a point to) so what would the insurance company do?