Heck that's bad luck, I feel for you.
Trying to be practical, the first thing is have you got an agreed value insurance on the car ? Most classic policies do have and that would make things easier to argue with the insurance company regarding repairs, etc.
Bodywork isn't so tough, all the parts are available and unless the rules have changed you are within your rights to expect it be repaired at either a Lotus dealer (oh yeah) or approved specialist. Banks are the obvious ones but there are others who do full scale restorations & bodywork.
One thing that does concern me is if the damage is as far as the luggage tray then there could be damage to the rear of the chassis legs. That could prompt an insurance company into declaring it a write off. If they try that route then it's important to make sure it's not classed as a complete write off, never to be rebuilt, etc.
If the other insurance claim it's not economical then there might be the option to buy the salvage and rebuild yourself. Hence the write off category will be important, if only because we don't want another Europa permanently removed.
As for dealing with insurance companies, I am assuming your insurance company is going to claim off the other party ? Although it's many years ago, we were rear-ended at a roundabout (wife's brand new car, less than 200 miles on the clock) and it was the first time I'd ever had to make a claim. In that instance our insurance company appointed a legal firm who gave us loads of forms to fill in, after which it all went away.
The legal bods made sure the 3rd party paid our excess, apparently very important for future insurance purposes, so make sure that happens. They also insisted the car was repaired at the main (supplying) dealer rather than a body shop appointed (approved ? huh ?) by the other insurance company.
So if that's the deal you've been offered, it worked out ok for us. Car back as new, no outlay and they even came back with compensation, something I never thought of. Check out exactly what they're offering and why, it might be similar ?
Brian