I think that the answer to this question is dependent on how the reader views the contexts that have been outlined. If the reader is more inclined to view the world in the constructs of a September 11 "nostalgia," as Changez puts it, there is more likely to be a rendering that one character kills another. If the reader is more inclined to view the world in constructs that lie outside of strict readings of terrorism and fundamentalism, I think that different conclusions can be reached. The key element in this is that there is discussion that emerges about what conclusion can be seen in the end of the novel. This becomes Hamid's primary point, believing that discourse and discussion about fundamentalism and terrorism are needed in order to do something about it. Is Changez a fundamentalist/ terrorist because he asserts Pakistani independence from foreign aid? Is the American prone to violence because of how Americans are perceived to view Pakistan? I think that there is much in way that either of the three endings could be evident. The fact that the entire novel is one long discussion helps to bring forth the idea that the ending is secondary to the discussion about it, something that has been missing in the understanding of fundamentalism and terrorism. If Hamid is right, it is through discourse and discussion that such elements can only be understood and the violence associated with them stopped for good. In this, the ending becomes one of discussion.
Based on the fact that Changez mentions homosexuality at least four times during the conversation, I think that Changez' dinner guest simply says to Changez, "I am not not gay, and you should hook up with someone else."