This is quite a big question and it requires interpretation. The meaning of Gatsby's death is not clearly stated in the text, nor is it articulated by Nick. However, there are several compelling readings available to us based on evidence that does exist in the text.
Gatsby's death can be seen as the consequence of his relationship to "reality". Jay Gatsby, in his life, does not merely accept reality as a given. He sets out to change it. We can see this in the persona he adopts, the facade he constructs, behind which he stands gazing out, as he did from his balcony when Nick first saw him.
Gatsby fabricates an identity for himself, a false one, and attempts to convince the world to believe it. In a sense, he is attempting to shift reality according to his will. This is true as well in his relationship with Daisy, as he tries to rebuild the past, despite all that has happened over the years.
Concerning his behavior with Daisy, Nick tells him he can't repeat the past. “Can't repeat the past,” Gatsby replies, “Why of course you can!”
This way of relating to reality puts Gatsby at odds with his world. He wants to have power over what is real. In the end, the world asserts its dominance. The dreamer who believes his dream to be more real than reality is forced to wake up. This reading of his death is in keeping with the argument that Gatsby's "primary flaw was a naive idealism".
We can also see Gatsby's death as the natural moral or karmic consequence for his criminal behavior. Though Gatsby does not die as a direct result of bootlegging, an argument can be made that he was due for a fall. He had enemies. He was a criminal. Justice was bound to find him eventually.
After all, he is a bootlegger, a man with unsavory underworld connections, a fraud in the sense that he misrepresents his origin.