"un-economic repair" is what the insurers call it....... It doesn't mean that it can't be safely repaired, simply that in their view it's easier to pay you up than repair it because it's so old and the bottom book price is next to nothing. After all, we ALL know that the first question that a repairer asks you is: "Is it an Insurance claim"
(Which means costs X 2). It's an Insurance write off - not a damage write off.
Go for the best that you can get, plus... say that you want the car back as well......It'll cost you half to get it fixed, and you'll have a free holiday with the rest.

Last time we tried that we ended up 2 grand down and had to make our own arrangements to collect the old one after the insurance insisted on towing it to Essex to examine it.
Currently waiting for a reply having sent a quote directly to the 3rd party insurers.