I think the transition away from cars will be slow enough that this wont be a problem. In the ideal situation, people will just stop replacing their broken down cars.
We already deal with it somehow. Scrap them for metal, recycle rubber and probably just throw away plastic, because plastic recycling is pretty crappy.
Yeah that's probably true, but we will need new stuff. More public transport like trains and so on. I would assume that we can recycle quite some stuff there.
Also a lot of other things need these resources and I am sure that at least a lot of the could be used to enhance the world further