Both have zero chance of dying.
Naruto;
1. must become Hokage (or the series is pointless)
2. must save Sasuke. Why? A couple arcs would be pointless if not. Naruto never breaks his word. Everybody comes around to Naruto's way of thinking eventually, since this is his story after all. Yes, Naruto wants to save everybody. That has always been the case. That doesn't mean he's given up on Sasuke
Sasuke must overcome curse of hatred by showing the world Uchihas are not evil.
1. Or Itachi's sacrifice and entire character arc is pointless
2. Lots of Naruto's actions would be pointless (see above)
3. Themes like overcoming the mistakes of the past would be pointless if Sasuke doesn't overcome the curse of hatred
4. Sasuke is very slowly crawling his way to redemption. It would be be pointless to kill him now.
Kishimoto said he hated to kill Neji, who is a minor character in Part 2. Thus, I don't see him killing the most or second most important character in the entire series that he was written for over a decade. He's too attached to the characters for that, if it was difficult just to kill Neji.
Naruto is a very idealistic story, despite having dark moments in the middle. I only see a happy ending. Obviously if either character dies, the ending will be bittersweet at best.