New bumper, crash bar (just to be sure) and rear light should just about cover it

assuming the boot lid lines up all the way round, and still opens/closes as it should

If they start getting evasive, take a cheque for £600 plus you keep the car

very easy DIY fix, looking at maybe £120 max for second hand parts and an hour of your time if it comes to it
BUTShouting as it's important...
DO NOT, UNDER ANY CIRCUMSTANCES LET THEM TAKE THE CAR AWAY. THIS MIGHT BE INCONVENIENT FOR YOU, BUT HAVE IT ASSESSED AT HOME EVEN IF THEY SEND THE ASSESSOR OUT. THEN GET THE CAR ASSESSED INDEPENDENTLY BY A BODY SHOP YOU TRUST. THEN WHEN THEY AGREE TO THE REPAIR THE CONDITION IS THAT YOUR BOIDYSHOP DOES THE WORK AND THEY AGREE IN WRITING TO PAY HIS BILL AS AGREED FROM THE ESTIMATE HE GAVE YOU. THAT WAY THE CAR IS DEFINITELY REPAIRED, RATHER THAN THEM TRYING TO WRITE THE CAR OFF.
If they refuse take a settlement but you keep the car. I suspect they will try and wriggle as the repair will coist them about £800... £380 for the bumper shell, £50 for the crash bar, £100 for the light, £50 for a litre of paint and the rest in labour...