Well the car wasn't going very fast. Obviously for it's reasons. So I dont think a person would die from that speed. However if he's going a normal car speed, and he hits that Joker, Joker definitely has high high chance of death or near death damage to his body considering he already had a very weak body.
@supreme_marvel: I am mostly asking because the windshield broke in the scene. How much force is required to crack the windshield like that? Is it a lot or not that much? Joker shrugged it off for what's it worth. Pretty sure irl during filming they just used prop glass.