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.
"I'm not gonna lie I'm really looking forward to heavy kissing and touching between these two with these haircuts" I'm going to blame that comment because this is totally its fault. ~Lol the unicorn screen saver loves it!