I suggest that until all the car parts like a clutch, transmission box, ect. don't have their damage models (or how to call it) done, there should be at least some simple overall damage model aside from the visual one. The most simple I can think of right now is that the a car would be said to be KO, if some noticable damage would have been taken.. like in % or parts - depending on location of the part in the car, and on the location of the damage taken. It just sucks in such realistic simulation to have cars hitting the walls in 200 kmph and then drifting away.