Someone needs to go back and watch the beginning of the movie. If the entrance doors are taped when the firemen break them down, you know he never left.
I watched it last night, and went back to watch parts of it today. It is a film that requires you to be attentive, especially to the layout of their apartment. In the opening scene, the firemen break in and find both doors to the master bedroom taped shut from the outside (which we later see George doing). Presumably, he did this to keep the smell from getting out into the rest of the arpartment, because he also has the windows open in this room (one of the firemen opens a window in a different room when they enter the apartment. The smell is obviously strong enough that it permeates the whole apartment at this point, which would suggest the body has been there a while.
The last scene in which we see George, he has moved to a spare, second bedroom off the kitchen, at the opposite end of the apartment. It is here that he gets up from the bed and sees Anne, renewed to health, and the two walk out of the apartment together. Read this scene as you will, to be a dream, or a suggestion that George has laid down and died (which is my reading), but I don't see how it is consistent with an interpretation that he "runs away" in the end (the look of surprise on his face when he sees Anne suggests that he does not understand how it is possible).
The final scene is indeed set after all the other events of the film. The shot is framed so as to show both bedroom doors with the tape removed, and the place looks cleaned up (the bed is stripped and all signs of being "lived in" are gone. It looks basically like a show home. She is an orphan, and the ghost of her parents' legacy lingers in the empty rooms.