I would also say take the £600, the car is a 2.1 petrol so is less desirable by those of us that want a big engine in a Jag.
Regarding the wing and bumper, a secondhand set of items for £150-200 and you'd be golden or better still green if you found the replacements in the right colour. Put a new MoT on and you might be able to ebay it for £1000-1200, maybe a little more on a good day.
Second option of repairing the body damage and a new MoT and selling it yourself is a lot of work for little financial gain (if any) whereas the dealer offering £600 is taking those risks but also stands to gain more when he sells for £15-1800 all bright and shiny like a new pin....... errrrr Jag even. The problem is, once you start digging to fix the body, you might find other bits that suddenly cost in limb proportions, while i understand that with it being your late fathers car there is some sentimental attachment, sometimes you have to be cold and clinical and evaluate the situation to your best advantage.
Good luck with whatever course of action you decide to take.