Well, if Sasuke had died,m there wouldn't be much of a storyline. Either that, or we'd actually get to see more of the Naruto Univrese(that would be fantastic!!).
The effects vary depending on when he did:
If Haku killed him, Naruto would be really emo for a while, but would eventually learn Chidori. And Sai would've been introduced earlier, and might *gasp* even be likeable!!
Against Gaara, more or less the same as the Haku incident, only Naruto wouldn't have a reason to learn Chidori.
Against Orochimaru, Oro would be the most badassed villan of all time. 'Nuff said.