1. The calculation of damage that a party is liable for is the pre-accident value, less the post-accident value. It can be argued that, for the pre-accident value, the value that you would have received if you sold the vehicle on the day of the accident may be used. So, it can be argued that retail value and not book value is to be used.
2. In terms of your contract with the insurer, you need to check whether you are covered for book value or replacement value. It is normally the former, although some short term insurers do offer the latter.
3. If, however, the insurer pays you and you receive the money, your claim for damages then belongs to the insurer in terms of the rule of subrogation. In other words, your insurer has the choice whether they want to instigate action for damages on your behalf. If they do and they win, then they need to pay you whatever they get in excess of what they paid you. If you claim without them having ceded back the claim to you and you claim for only the difference between what you received from them and the retail value of your vehicle, then the insurance company cannot claim against the negligent party their loss. Which means that they are going to claim everything they paid to you, back from you.
4. If you want to instigate a claim, you need to get permission from your insurance company and get directives from them what will happen if you win the case.
So, in summary: You can claim for the retail value less the salvage value of your vehicle from the negligent party ONLY if you did not claim from your insurance. If the insurance company pays out, your claim for damages against the third party is for the retail value less the salvage value less the amount received from the insurance company. That you can claim ONLY with the written permission of your insurance company.