Interesting theory, Yondaime, one i hope they'll run with, but i doubt Sasuke is in it for anything but pwer to fullfill his revenge. I might have seen it as a viable theory if Sasuke hadn't bumped into Itachi. Before his run in, he had managed to form friendships, to openly (debatable) care for people. But when he underwent that Sharingan torture and saw how outclassed he was, whatever semblance of a life he had managed to scrape together, whatever loyalties he managed to form where instantly forgotten. Only thing that remains is his need for revenge. He just wants the bastards head on a platter, no matter the price. And the quickest way to get his revenge is by selling his soul to Oro.

Neji-Anki-Sama goes with the assumption that Naruto will bring back Sasuke, either by dragging his unconcious body or by convinving him to come back.
But i don't think that Naruto will be able to fullfill his promise to Sakura, at least not right away. I think that Sasuke either manages to lose Naruto, someone intervenes and stops Naruto from pursuing Sasuke,
or most likely, Sasuke just plain beats the crap out of Naruto. This would be a severe blow to Naruto, because so far, he's managed to pretty much touch everyone with his ideals and optimism, from bad ass ninja Zabusa to neji to Gaara. It would be be an intersting side story to see how Naruto deals with "failing" his friend and team mate Sasuke. Either way, after that, we have several alternatives, if we operate on the assumption that he'll be saved.

1. Sasuke kills Itachi, and then leaves Orochimaru because his task for vengance is done. Provided of course, that Sasuke trains his ass of with Oro, otherwise he won't be able to stand a chance against his brother.

2. Naruto and co manage to beat some sense into his skull when (or IF) the leaf deals with Orochimaru.

3. Sasuke realises how much his friends means to him (maybe after Sakura is injured, or Naruto abducted by Itachi), and leaves Oro.

4. Sasuke finds out about oros plan to take over his body and leaves.

5. Orochimaru is killed, thus realising the seal on Sasuke and Sasu goes home.

Personally, i think (and hope) it'll be either option 2 or 3. And i'm quite sure that Naruto will have a hand in Sasukes return to Konoha, thus, ultimatly, fullfilling his promise to sakura. That is, IF Sasuke returns to Konoha, which we all hope he does.