That's no excuse though, for damaging someone else's vehicle and just driving off. Assuming that the driver of the vehicle actually knew they had been involved with a collision.
They could not have not known by the bang, it is fairly obvious if you have hit something at any speed, they braked and so did I but there was no sensible place for either of us to stop unless we were half a mile apart and then who turns round, me, him or both of us. that is why it is difficult to know what to do in those circumstances, a more serious thing then one would have no option but to stop. Anyway the outcome was not so bad, took it to a pal who said these things are designed to come off rather than smash to pieces and probably damage the door also it should all go back together and as long as the electrics are OK and the motors still work all you need is a new glass for about £20. Job done in about 10 mins.