The register keeper has failed to declare who was driving the vehicle at the time, and has been dealt with accordingly, and so it remains that the individual driving is unknown. This is no different to situation you were faced with at the very beginning when the driver buggered off leaving you picking up the broken pieces. The police investigation has taken all reasonable steps to find the driver and with no admission or declaration by the registered keeper it will have come to its natural conclusion, for now. You have correctly updated your insurance company and it will now be down to them to accept the findings of the police enquiry and look to compensating you for your losses from the pot of money set aside for situations such as these. You should, by now, have had contact from one of their assessors and a report completed on what your losses are. I would give them a week and if nothing is heard from then, get on the blower and stimulate their backsides with a metaphorical boot up it!
Hopefully all will be sorted for you soon. @tu*