UPDATE....UPDATE

Well, we have good news.  No, British Air didn't send a special flight just for us, but they did refund all of our airfare.  The car rental refunded everything we paid them as did our hotel in London.  Also the Mac's Adventures, with whom we booked our walk, refunded 50% of our fee.  And today, the trip insurance folks, Allianz Global Assistance, approved our claim in full and in 10 days!  The have already deposited the funds directly into our bank account.  So when all is said and done, we only lost the experience of going, we didn't loose any money.