Who's car is it ?
Exactly it is YOUR car, no insurer can "write it off" unless you agree on a settlement, as it is your property and not thiers, you own it not them.
If they write it off it becomes thier property as you have accepted payment for it.
So therefore ONLY settle on the basis that you keep the salvage, which if very old will be the scrap price.
Remember they cannot settle unless you agree, they cannot just send you what they think it is worth, the most they could do is ask that you sign a disclaimer if you buy the salvage.
Done this 3 times, last car had £428 worth of damage, was going to be written off by insurer, but instead I opted to take repair costs, AS ANYONE HAS A LEGAL RIGHT TO, still not repaired as only a slight cosmetic dent in 1/4 panel, and car is still insured with same insurer on same policy.
If the estimate comes back at say £500 you are entitled to have the money paid to you and choose whether to repair yourself, leave as is(if driveable) etc perfectly legal.
tabetha