Did Mr. 17C squeeze into his partial seat? I think the thing to do would have been to wait until the heifer fell asleep, stuck an apple in her mouth, then you and 17C could have enjoyed a luau until she was down to reasonable proportions.
I guess that's a little insensitive. Few people get so morbidly obese for medical reasons; it's lack of discipline. That's their prerogative of course, unless they try to force the rest of us to pay for it. My mother has had a "glandular condition" ever since I can remember, and when she decided to lose weight she went on Atkins. Surprise: it worked. It worked for me as well, although admittedly I had no medical condition to "blame."
Obviously the OP was treated abysmally. The crew was only concerned with their own logistics and not the torture they were about to inflict upon him for a 10 (?) hour flight. To the OP: this is a serious (albeit unusual) problem, and I hope you can convince CO that you are not looking to be bought off with a few goodies, but rather want them to develop a more sound contingency plan for these situations.