The car crash disfigured the car into something people wouldn't really call it a car anymore. However, even if earth stops supporting human life (or, more likely, greatly reduce the number of places on earth that humans can live on), no one would argue it is still a planet.
I think that assertion is disproven by thinking about what junkyards are full of: cars. It doesn't matter that they can't drive anymore, or even that they may be totally missing significant parts. People still generally think of them as cars.
