Well, you might have a point, as I don't think kishi would kill the most important chars unless he kills both. But either way, it's likely that even if he does that, they'll return somehow. He's not gonna take them out of the series.
They are most likely gonna die together, Naruto never predicted it
well he did and didn't so to speak. Naruto predicticted that if they fought EACH OTHER they would die. But yeah, I don't think he predicted that they would BOTH die at the hands of a man who should have been dead a long time ago
Kishi makes this short moment more dramatic than it would have to be. Before Sasuke dies he could always just use izanagi. As for naruto, I don't actually know but since Kyuubi/Gaara has a plan for him I'm sure we'll find out soon enough.
Will they die together? Sometime maybe, but not yet.