Hell, Naruto himself might be pissed at Tsunade, maybe even Shikamaru with how things transpired.
I found it rather weird that, at least from Naruto's perspective during the chase, he felt as if he was trying to 'rescue' Sasuke. I fully believe either no one directly told him that Sasuke left on his own (Which I certainly didn't see after re-watching the episodes in question), or there was a miscommunication down the chain of command.
Shikamaru, during the breifing outside the city gates, made it sound like this was a rescue mission, as in Sasuke had been kidnapped. Certainly points to that when Naruto was running after Sasuke, leaving Lee to Kimimaro, and asking himself 'Why is he running away?'
I mean, what do you think would change if everyone who went after Sasuke knew with 100% accuracy that Sasuke himself had left the Leaf? When he left the village like he did he became and official Missing-nin IMO.
Meh, I'm blabbing. I can certainly imagine Naruto being shaken up by something like this, even so far as changing his 'Never break my promise' attitude. It's a good ideal, but his promise to Sakura has already been tainted with the death of Neji and Chouji. While he wasn't 'close' to Neji, Chouji was part of the group of misfits he hung out with during the academy days (Shikamaru, Kiba, Chouji, and Naruto) and one of the few people during that time that actually acknowledged him.
Fuck, if I was Naruto, I'd simply straight up say. "I'll kill every last Uchiha on sight!" (Seeing as there are only Itachi, and Sasuke left, it's a good promise. Unless the rumors about the AL having Sharigan is true, but that doesn't really change the facts.)
Seriously. Nothing says focus like the death of a close friend (well as close as most of his friends could be).
Frankly, I'd be scared to even look at that AU Naruto. He'd almost be making himself an 'Avenger', maybe, bah. Extreme case, anyway.