Aleks,
What a dreadful occurrence. The most important thing is your partner's health - and it sounds as like he will be ok.
There are a couple of issues here: as always, if you don't like the first answer you get, call back. Of course, you have many more pressing things to deal w/right now than stay on hold w/AA - but it is worth a try. Also, if you haven't done so, offer to provide medical documentation of his condition - others have had success when providing something more official than a phone call.
As for a compassion fare (which I haven't heard of): in all honesty, you can often find less expensive options online. I did a quick check on AA.com and you could book a round trip ticket leaving London on the 11th for $620.00 rt. (JFK-LHR-MCO). For an int'l ticket booked 48 hours in advance, that's a very good price.
Again, my thoughts are with you and hope that this all works out for the best.