Obviously his son will be very upset about the loss of his father, but he doesn't care(people who are this screwed up in the head never do.)
While I agree that people who are screwed up in the head are totally self-absorbed (especially suicidally depressed people in my experience), it is not like the guy is dying. He/she/it will still be there for his son, and presumably be able to offer a unique (not necessarily valuable) perspective on life. I think the selfishness is primarily in getting married and having a child when you are in that position, not in going ahead with the sex change. I mean, regardless of whether or not he gets the sex change, his issues will still be there.