Your insurance company has a duty to tell you which Salvage yard they are going to sell your car through. If they don't I can find out for you mate as it will be one of 2 places
The £13k repair quote is obviously with new parts, so a new crate engine, wiring and modules from Nissan etc.
They also have to tell you what category your car is (now the insurance companies if they have paid out).
If it was a good one then buy it back and drop an engine into it, if not then I may bid on it if your ok with that?
Best regards,
Lee