imo, itachi won't get to say anything to sasuke. i mean seriously, think about it. Itachi and Sasuke beat Kabuto, then Itachi convinces sasuke to back off the village? that would put a serious dent in the storyline.
no, what i think will happen is that kabuto manages to stop itachi. thus, itachi breaks his promise to sasuke, and sasuke goes back to the darkness.
Yeah, I'm really at a loss as to how Sasuke's dark side is going to re-emerge. I've got two theories but they're purely speculation on my part.
1) Kabuto summons Sasuke's parents using the Edo Tensei.
Since Sasuke's father (not sure about his mum) supported the Coup, they might persuade gullible Sauce to continue on his mission of vengeance. Kinda like the ending of Spiderman-2 where the dad guilt-trips his son to keep fighting the protagonist. Sasuke's dark side emerges and completely ignores what Itachi has to say going after Naruto once again.
2) Before Itachi fades away, he tells Sasuke the full truth about what happened that night. We know that Itachi wanted Sasuke to live a life of vengeance based on the killing of the clan. We also know that Tobi is one helluva good liar. The only other confirmation we've gotten about the Uchiha massacre is from Danzo (who may have been present, before the Sasuke-Danzo fight, Tobi says that he hasn't seen Danzo since the massacre).
Itachi reveals that it hasn't he who killed his parents or the clan but Tobi and/or Danzo/otherleaftopbrass. This way, Sasuke would still have his hatred for the village but also for Tobi which would compel him to go to the NarutovTobi fight and mess things around.
You're right in saying that if Itachi convinces Sasuke to be good again then he wouldn't fight Naruto or make it to the final battle which means that something has to make him angry/insane again. Since "The Truth" keeps popping up in the latest chapters, something tells me that Itachi's real spin on the story will do this.
