That’s slightly unusual. Usually insurers have in house engineers who determine total loss value from Parker’s, Chaps and Browns etc. It’s basically a blue book guide with a range from poor to excellent. They usually go in the low end first. Sounds like you had a better experience than most and...
If repairs are over circa 60% of the market value then yes, it will be written off. Delays on parts coming from the EU post brexit mean people are in hire vehicles longer thus pushing up the cost of claims. Some parts are just not available so the insurer has no choice but to write off.
Third...