For those surprised by George's reaction to Susan's death, here is a theory:
This, I understand, is Larry David's last episode; he's leaving the show. The events may be a Larry David wish fulfillment.
We know that George is based on David. Did David dislike the Susan character enough to want to kill her off? Was he happy to get rid of her?
Perhaps George's reactions do not represent the feelings of the character George towards his fiance whom he has fallen out of love with, but of the writer David towards his character Susan whom he has fallen out of love with.
The only reason Jerry and the other writers put up with this storyline was as a tribute to David's leaving.
At least, this is the most rational explanation I can think of for George's insane response.