I think Harry will end up killing Voldemort as we all expect. But I don't think it will end up being as simple as that. All the horcrux have to be destroyed in order to kill Voldemort. If Harry is a horcrux, at the end of the story his will probably be the only remainig horcrux to destroy. How Harry will go about doing this will be something to read about.

Harry does not yet know that he is a horcrux neither does Voldemort I exepect. I think that Dumbledore may have known or suspected this. Dumbledore was the one who pushed Harry to learn more about the horcrux. Why? Why did little Harry have to learn about the horcrux when there were many more able and well trained wizards who could do with some knowledge about this (assuming of course that very few knew about it)? Also why did Dumbledore take little Harry with him to destroy a horcrux which was guarded by inferi and a countless number of hexes. He could have taken anyone more trained or no one at all. I think this was all in preparation for Harry to learn the truth about his scar and the ways to deal with it. I think that Harry is expected to find out for himself that he is a horcrux. It will in the end be Harry's decision how to deal with this fact. When all the other horcrux have been destroyed, it will be up to Harry to decide how to destroy the final horcrux.

I think that Sirius will come into play here through the two-way mirror. I think that Harry will do something very dangerous to himself but there will be a way back and Sirius will be his guide.