I'm no expert but isn't there a GAP product that will give you a replacement car not just a return to invoice version.
Not sure if this is a brand new replacement but worth a phone call to Car2Cover or a similar provider.
Vehicle Replacement Gap Insurance
What will it do for you?
“ In the event of an insurance write-off as a result of an accident, fire or most commonly theft, our Vehicle Replacement Gap Insurance will pay the difference between your motor insurers settlement – and the cost of a replacement vehicle matching the original vehicle specification, age and mileage – even if the replacement cost is more than you originally paid. This cover is suitable for cash and finance customers.“
This insurance is not available to everyone. Please refer to ‘Can I Buy It?’ below.