I think if Sasuke ever had killed Naruto. Naruto would have definitely kept on smiling. I also think that Naruto smiling after Sasuke killed him would either make Sasuke turns his ways around, or it would fuel his anger even more.
When you get this tall, you can become Hokage. -Iruka i think this was the best flash back by far. especially cuz it didnt include stuff from previous episodes,, which get annoying in the middle of a battle.