Why did Flitzgerald ''kill off'' Gatsby?
By killing off Jay Gatsby, Fitzgerald makes an important point about the American Dream—specifically, that a dream cannot survive in the harsh world of the 1920s. Remember that the novel is really about Gatsby's dream to be reunited with Daisy. Everything that Gatsby has achieved has been done with one purpose: to win her back. His death, however, brings this dream to an abrupt end, providing definitive proof that Gatsby's dream will never come true.
In addition, Fitzgerald also uses Gatsby's death to make a wider point about wealth. That is, that no matter how much wealth and prestige a person has, tragedy can still happen. In other words, no amount of money can protect a person from the evil intentions of another. In this case, money offers no protection to Gatsby from George Wilson, a man determined to have revenge.