Firstly sorry to hear about your car being written off.

It depends if you have a claim against your Insurance company or a third party ?

You'll not get the money back as such, but a service bill is supporting evidence the car was properly maintained and such should be reflected in the valuation.

I've never been in this situation, but I understand the insurance quite often makes a low offer initially, presumably since if accepted their profitability increases, so expect a bit of haggling here.