First of all, sorry to hear about your partner, and it's good that he's out of surgery.

I'm not sure what really can be done. AA didn't issue the ticket, and as such would be very limited as to what they could do with a booking which was issued on BA stock.

As for the Avios, you might be able to persuade BA to refund some given the circumstances but I'd imagine that would be a goodwill gesture on their part. As for the cash - well, unfortunately, I can't see AA giving you anything back and BA certainly won't in this circumstance.