Watch a movie based on actual events, and nine times out of ten, it'll have a section before the credits telling you what happened to the real life people the movies is based on. You can check out this clip from The Pianist to see what we mean.
The final chapter of World War Z, titled "Good-Byes," works like those brief bios at The Pianist's ending. We get a bunch of really brief sections letting us know what the characters have learned from the zombie war or what they're doing now that things are returning to relative normal. These sections also help tie up the thematic threads Brooks set throughout the novel.
Here are a couple of examples:
• Mrs. Miller continues to be a mother now that the zombie war has come to a close. (Yeah, that's kind of the way it works.) She mentions, "I'm the American system, I'm the machine" (9.5.2).
• Kwang Jingshu's ending informs us that he's still caring and sharing as an awesome doctor.
• We never hear from entrepreneur Breckinridge Scott after his interview, but Arthur Sinclair mentions the government is interested in extraditing him to the US, suggesting a wee-bit of comeuppance for this unscrupulous character.
• Johnny Clegg's good-bye suggests the darker side of warfare as the character can no longer live a life without the thrill of the kill (9.3.3). On the other hand, we learn that "Mackee" MacDonald might just be making peace with his own warfare experiences (9.3.10).
• Michael Choi's final hurrah plays on the natural effects of the zombie wars. Here, Choi mentions how the zombie plague disturbed the natural world just as bad, if not worst, than the human world, especially if you look at it from a whale's perspective.
And so on. Each good-bye gives us some sense of closure, whether it's thematic closure, plot endings, information on a character's future, or some combination of the above.