Thanks everyone.
My father passed away Sunday, May 20.
I had spent two weeks back home in Washington with him, basically watching and waiting but finally had to return home for work. My father died four days after I got back to London. And I can't afford to go back home again for the funeral, but at least I got to see him and say goodbye while he was still alive.
While I was in DC, I changed my return flight twice. United was completely unsympathetic; they charged me $250 each time I changed the ticket ($150 change fee plus difference of the new ticket fare). And all the direct flights back to London were full, so I had to fly from Dulles to Boston to Frankfurt to London.