You have to inform your insurance company that the accident has taken place after, you have no choice on that you can then chose to let them proceed to sort the claim out or you can go straight to his insurance company. If as you expect they will write the car off you then reach a settlement with the 3rd parties insurance company as to the value of your car, you can let them know if you want to buy the car back under a salvage value, once you have agreed that you either buy another car or you get your car fixed. From today you are entitled under a Non Fault claim to have a hire car or an agreed amount all the time you are without a car, this will cease once you have either repaired your car or bought another car.
One thing to remember should you buy your car back under salvage values your car will be registered by the insurance co as a Cat D or might be a C but I wouldn't think so with the damage you have described.
Check your policy for free legal advice as a lot of motorists have this but either pay more at the time of crash or do nothing at all and all because they were unaware they had this facility. Check also your Credit/Debit, AA/RAC cards as these often have free legal cover. Any injuries can be dealt with either directly with the 3rd parties insurance co or through a solicitor which is the better option. You can contact a legal co that deals with these type of claims and they will work for you on a No Win No Fee basis. The fee these days is normally a percentage of what they manage to win for you but they will guide you through a a legal minefield.
All that said I feel for you, I know its only metal but we do fall in love with our cars. Hope the above is of some help to you. Mike.