Hi Chris, I'm shocked and really gutted for you, I know what a lot of effort and a great job you had done on GW. I hope that in time you manage to find a silver lining to this black cloud, and end up with an even better MK2 80, (think of those times you said 'if I did it again, I'd do it slightly different...'). Keep your chin up, mate.
With regard to GW's remains, you may find that the vehicle is no longer classed as such and is now, in the eyes of the insurance company and the authorities, classed as hazardous waste. As I'm sure people are aware there are lots of materials that make up a car and once they are burned some of them can be quite hazardous to your health. With this in mind it is normally the insurance companies policy that vehicles that have suffered a substantial fire, are hazardous and nothing from that vehicle is reusable, (assessing individual components would be a difficult call for them with regard to future liability and cost wise), so their remains are sent straight to the crusher. Going on your initial description it would seem that GW maybe too badly damaged to escape disposal.
I know in most cases if you keep hold of the car, you have a good chance of retaining the salvage after the claim is settled, but in the case of fire the insurance company, your neighbours, the fire brigade and even you and your family may not want the burned remains sitting on the drive for very long.
I known a couple of modified 4x4's that have been lost to fire, one was at the side of the road, so it was never seen again and the insurance co wouldn't allow anything to be salvaged. The second was fire bombed outside the owners house (mainly interior damage), it took a lot of effort to get the insurance to allow the vehicle to be released to a specialist 4x4 garage, to enable them to remove items like bumpers, winch, guards and long range tanks. This was probably only in the insurance companies interest as they could pay out a little less if these items were recovered. They only allowed the specialists to have the vehicle for 48hrs before it was crushed.
So if I was in your situation, I'd take pics, and then promptly salvage anything I could, roof rack, roof tent, spare & rear wheels, on board air, rock sliders, under body guards, rear axle (or at least the rear diff), you may be able to salvage the front diff (the axle may be too damaged) and winch bumper but it may be quite hazardous. Plus possibly the rear tailgates and some interior parts? Then I'd let the insurance company send the base vehicle away. After all you may need to claim for the damage to your drive as well as GW.
As has been mentioned, print out all the ad's for 80's, especially the expensive ones, and make a big thing about the low mileage and excellent condition of yours when trying to get what it was worth out of the insurance. As your well aware there's a massive difference between a good 80 and a worn out one.
Sorry for the long post, I hope some of it proves helpful. Fingers crossed for you. Shout if you need a hand to salvage stuff fast.
All the best.