In reply to Big Jim The Climber: Look into the Motor Insurance Bureau (MIB) which was set up to cover this type of incident. The witness statement will help prove that it is a genuine incident, rather than an own-fault.
You'll have to pay your excess initially, but may get this back. You're talking years rather than months though.
Pester the police daily for progress with their investigation, otherwise it will never be resolved. If they find him but don't charge, push your insurance company to take out civil proceedings, or else they are also likely to try and take the easy route out - they already have your money.
Details available via Google.