If I were really crushed and there was no other seat available, I'd have stood most of the time (or sat on my bag in the galley, more likely, since I can't stand for long due to injuries) with lots of apologies to the cabin crew for getting in their way, had that fact put on record by the SCCM, and asked for a goodwill gesture from BA on the basis that I did not get a full seat (because once we take off, and the flight is full, there really isn't much that can be done about it).

I'd however ask to be offloaded if still on the ground in the absence of a solution, although I'd feel terribly bad about causing a delay due to having to find my luggage. I cannot stand for long, so it would be a very unpleasant flight if I had to choose between standing and being crushed, so the only solution is to get off.

I don't think I'd have taken them to court for an injury incurred, by preventing myself from suffering a long-term injury in the first place (by not being in that seat). But I can see it can probably be a bit more awkward for an infrequent flyer to decide what to do in the situation.

When I got crushed on VS (many years ago though) by a very large man next to me, they put me in a cabin crew jump seat for the cruise. Rather upright, but still better than being crushed.

So do BA.