Death can of course be considered the high cost of living. The spirit of the stairway is a literal translation of the French "l'esprit d'escalier", and is explained by Sexton (who we will meet soon) on page 23.
The skyline suggests we are in London.
It's June. This is Mad Hettie, who we have met before in issues of Sandman. She normally resides in London.
Capturing birds after feeding them rum raisins is a method used for poaching in the book Danny, the Champion of the World by Roald Dahl.
A haruspex is a fortune teller of ancient Rome who foresaw the future using the entrails of freshly killed animals.
"Quid" is English slang for pound.
"Effing" is a euphemism for "fucking" as an adjective, roughly equivalent of "bloody". A finnie is a 5 pound note.
A sovereign is an old English gold coin worth 1 pound.
I don't know if this is a reference to an existing movie.
Mad Hettie is (at least) 250 years old. In Sandman #3, which took place in late 1988 or early 1989, she was 247. Hence the story takes place in the summer of 1992 (the comic is cover-dated March 1993).
Mad Hettie predicts the future like a haruspex should.
It is now July, and we are in New York.
Traditionally, superheroes have faithful sidekicks. Sexton is actually indicating that he isn't a superhero.
So, we have a possible suicide coming up.
Sexton is correct. Most suicide notes, most suicide attempts for that matter, are a cry for help.
People that cannot move or communicate are often described as plants or vegetables. There is a certain analogy between Sylvia talking to the plants on page 10, and Sexton talking to Billy here.
These are gulls. Gulls have adapted marvelously to humans. Originally, they were mostly present in the vicinity of large quantities of water, but nowadays they tend to be everywhere where humans are, and they seem to like garbage.
This appears to be Death. That would mean Sexton did not survive his accident.
By now we realize Sexton is not dead, since Death usually points out that fact to the persons she picks up.
We have also seen in earlier issues of Sandman that Death takes a person's hand when that person dies. Here she takes Sexton's hand to save his life.
Death living a few minutes away? Apparently this is not Death. It is possible to mistake someone for Death, even Delirium got fooled once (Sandman #41).
"Sewing things up" is an idiom for finishing or ending, which is Death's job. "You're really good at sewing things up" sounds very much like "You're really good at screwing things up", which is what Sexton was doing earlier.
The reference to family (emphasis in the original) makes it obvious that this is Death.
Slim and Wandsworth are really Death's fishes. You can also see them in Sandman Special #1.
Death explains what is going in. From Sandman #21 we know that she has to spend one day as a mortal in every century. Apparently, everything surrounding Death/Didi was created by "the universe" to allow/force that day to happen. Death has also spent a day mortal as a little peasant girl living near the Yangtze river (Sandman #47).
The universe did a good job.
Sexton explains "l'esprit d'escalier" - note that Sexton is indeed walking down the stairway.
"The spirit of the stairway" in action. The second observation Sexton makes describes the traditional view of Death as the Grim Reaper. Death having a penchant for playing chess with Scandinavians refers to the Ingmar Bergman movie Det sjunde inseglet (The Seventh Seal) (1957). The Internet Movie Database gives this summary (written by John Vogel):
A knight and his squire are home from the crusades. Black Death is sweeping their country. As they approach home, Death appears to the knight and tells him it is his time. The knight challenges Death to a chess game for his life. The Knight and Death play as the cultural turmoil envelopes the people around them as they try, in different ways, to deal with the upheaval the plague has caused.
Mad Hettie is using "gypsy" to mean "Egyptian", which is where the word comes from, although Gypsies do not.
See page 5 panel 7.
Mad Hettie claims she missed Death 100 years ago. That seems to indicate that the day of the century that Death has to live as a mortal is always the same one, or at least in the same year of the century.
Death/Didi didn't wear the jacket when Sexton left.
A smiley face button is pretty common. I might also be a reference to Watchmen, or to Boss Smiley, who we will meet in the World's End storyline of Sandman. A normal smiley face has no "cheeks" at the ends of its mouth, while this one has, and so do Boss Smiley's face and the Comedian's smiley. Watchmen is an excellent (and that's an understatement) limited comic book series written by Alan Moore.
Mad Hettie has lost her heart. We have seen people without a heart before. In Sandman #16, page 13-14, Rose Walker gives her heart to her grandmother, Unity Kinkaid. In Sandman #39 a boy named Vassily comes into possession of the emerald heart of Koschei the Deathless. According to the woman who owned the heart before Vassily, Koschei kept his life in that heart, but a woman stole it, and he died. Note that Mad Hettie is also very old, and apparantly also has a heart somewhere. If the heart being away from the body indicates immortality or anything like that (Mad Hettie is 250 years old), Rose Walker might also be immortal, or she might at least have stopped aging since she lost her heart. We already know that Rose is 25 years old by the end of the series, and looks like she is not even 20. The hearts in question are probably a metaphor for some of the essence of the person. In all three cases mentioned here the heart is not a real heart of flesh and blood.
Dylan Verheul wrote the first version of the Annotations. Sara Gray told me what a haruspex is. Tommy Kallio identified The Seventh Seal. Katie Schwarz corrected some silly mistakes I made. Pekka P. Pirinen provided some additional facts.