Part of where the story acquires its greatness is that the location of the story's resolution lies with the reader. The supposed worst in the reader has been awakened in the realization that Ali has become a fundamentalist. For a large part of the story, Kurieshi constructs it so that the reader is sympathetic to Parvez and his fears about his son. When Ali rebukes his father for his behaviors and then rebukes Bettina for her attempt at reconciliation, the reader strongly identifies with Parvez. We, as the reader, are with the father throughout, as Ali has been constructed in a fairly monolithic and one- dimensional manner. As Parvez approaches his son's room, we, as the reader, are still with him as some level of confrontation is required. However, it is Kurieshi's genius to shift advocacy in the most forceful of manners when we see Parvez beating his son. At this point, most reasonable readers would say that Parvez has crossed some demarcation and there is little in way of support that can be offered. When we are confronted with this reality, it is in this moment of reflection where the story "goes on." The reader must take the dynamic that is present between both father and son and leave the story assessing their own views. When Ali asks his father, cut and bleeding from the abuse, "Now, who's the fanatic," there is a moment where we, as the reader, have to assess our own views on terrorism and its perceptions of it. This is how the story goes on, for it continues in the mind of the reader. There are a multiplicity of paths that Parvez and Ali can pursue, but I don't think those are as important as the path the reader takes upon reading the story. In the end, this is where the story "goes on;" where we, as the reader, choose to take the lessons from it.
Taking in count the changes in both, father and son, I would say that they just keep going on fighting and discussing. Because Ali is already at a point where there is almost no way back, he is obsessed with all this stuff and he seems not to care about hurting other's feeling while he can in someway fight for Muslim's way of life and religious beliefs. And in the second hand we see that the father's mind is turbed and at somepoint it is difficult that he someday tries to change and behave as a real Muslim, because he has been living for so long not as one.
I could imagine a scene where Ali takes the rest of his possitions and goes somewhere else to live, with people of a Muslim comunity, where he would feel accepted and supported. Finding what was missed in his family.
In my opinion, something dramatic will follow after Parvez has beaten up his son: Perhaps Ali will leave the house. What will he do then? Maybe he will join a group of Islamic fanatics, but as Ali seems to be quite smart (good marks, he is thoughtful), I think he'll recognize he isn't helping any one with only accepting his perspective of the West. However, only if the father and son do compromise, there's hope for a good ending.