A lot of things die at the end of chapter 8 in The Great Gatsby. The most obvious deaths are the literal deaths of Gatsby and Wilson. Gatsby was killed, and when he dies so his grand dream of a life spent loving Daisy. Wilson kills Gatsby and then kills himself; when he dies, so does his modest dream of a life spent with Myrtle.
What makes this a holocaust, of sorts, is that both these men are innocent victims of faithless women and want nothing more than the simple love of those women. It's true Wilson murders Jay; however, he does it because he's been duped by both Tom and Myrtle. Gatsby died because he willingly took the blame for the woman he loves. The loss of innocence is a shattering holocaust.
The word holocaust is of Greek origin and means sacrifice by fire. Certainly, Jay Gatsby becomes the sacrificial victim of his amoral friends' actions:
The touch of a cluster of leaves revolved it [the mattress on which Jay lies] slowly, tracing, like the leg of a compass, a thin red circle in the water.
Then, Mr. Wilson's body is discovered as he has shot himself, also a sacrificial victim to the fire of his wife's passions, as well as one victimized by his environment of decay and desolation. And, both Jay Gatsby and Mr. Wilson are the scapegoats--just as the Jews of the Holocaust were scapegoats for the ills of Germany--for the decadent Buchanans who have refused to take the blame in the death of Myrtle Wilson as Jay is blamed for Myrtle's death. In addition, while Wilson is the murderer of Gatsby, he is also the Buchanan's scapegoat because eliminates a person who could have testified against them.