Sorry to hear about your sad news and wish you well for a speedy FULL recovery.
Insurance is a minefield, the offers are often very low. As it was not your fault ensure that compensation is also provided as your premiums will probably go up despite the non fault claim. It pains me when your pride and joy is destroyed by something beyond your control. If there are any nice items on the car its sometimes worth buying back to sell on items to offset the low payment.
I would do as Murdo suggests, find at least 3 adverts of like for like cars and email back advising them to revisit and fight your case. Surely its the BMW insurance that will be footing the bill so get your insurance company to fight your case. This is where glasses / CAP price guides are so unhelpful. I stressed last time I made a claim that they are just that - GUIDES not set in stone.
Good luck and I wish you well in getting this sad state sorted out.