I guess it all depends on the amount of damage and the repair costs, for me if the repair costs were say £400 you are probably better taking it on the nose and getting it done or getting the equivalent amount taken off you part ex.
If we are talking loads more then insurance may be the way to go, one thing i have found when claiming on insurance is if you let them know something has happened and you subsequently dont may a claim they log it as one anyway! , happened to us with house insurance when we were burgled so would be worth checking before you make you mind up