With my experience in accidents, no witnesses == you're screwed. I been hit 2x and both times it came down to a "i said he said" and the insurance of course didnt give me jack. Weird thing is... I called the police both times and they simply said "Everyone okay? Exchange papers? Okay, go on then"... and thats it. So go figure... sorry to say but unless he admits it, you'll have to eat your losses. Just hope he has to eat more than you.