Really depends on the level of damage tbh & whether the car will be classed as cat d or worse c & frankly based on high value (and more importantly availablity) of some FRS parts, especially the body panels, a lot of insurers wont want to repair the car even if you insist tbh

A lot of FRS parts are now starting to go discon/no longer available from Ford & some are on very long back orders which may not even be fulfilled which is what insurer will consider dependent on level of damage

TBH with the market value on the FRS dropping you'd be better going for a payout but remember as with anything if you believe they are not offering a reasonable amount i.e £5k when car in current climate should be £9k/£10k value then its a case of argueing with them & in the end you will get to a compromise

With regards to buying the car back & breaking it this is really only worth doing if you have the space, time, knowledge & tools to do it right & then spend a large amount of your time listing all the items on ebay Also worth considering that dependent on level of damage, how much is actually salvedgable undamaged for resale @ a reasonable price