I think that naruto will play some part in their fight though. Guessing by how the anime has gone so far, naruto will show sasuke that the power obtained with protecting people is the one that will defeat itachi, and thats how he'll do it.

The problem is that up till this point Itachi is the strongest ninja, who of the introduced characters so far, can only be beaten by jiraiya. He admits it himself that the best he would get out of fighting with jiraiya is them both dying, but anyways, i think eventually Itachi will become stronger than Jiraiya, if he isnt already.

But I cant really see this series ending with naruto beating the strongest person of all. Maybe Orochimaru will figure out a way to be the strongest, or another person will be introduced that is strongest of all and that Naruto will have to defeat. Anyways, it means that the end of this series isnt in sight, and i dont know alot of the manga, but i dont see there being any end to that either.... sigh