One of three things will happen.
1. Naruto dies, sacrificing his life to save Konoha and Sasuke from the darkness, sacrificing his dream because, as he said, "What kind of Hokage can't save even one friend. Right, Sasuke?" Naruto is chosen to be the 6th Hokage regardless of his death as an honor to Naruto, Sasuke taking up that position in place of Naruto as Naruto's equal. Sasuke spreads Naruto's story throughout the shinobi world, and at the final scene of Naruto we see two young boys with their sharingan active who Sasuke calls Naruto and Itachi.
2. Naruto and Sasuke both live, Naruto saving Sasuke from the darkness but Sasuke decides to have everyone believe he's dead, but works like Danzo did in the darkness, protecting Konoha from the dark. Naruto becomes the 6th Hokage of Konoha, fulfilling his dream and bringing the series to a conclusion.
3. Naruto and Sasuke both die, but Naruto succeeds in saving Sasuke from the darkness. Sasuke informs Naruto at that point he wishes to follow Itachi's footsteps and wants to be portrayed as a criminal. Naruto respects his wish and both exchange their final, strongest jutsu. Before Naruto dies, he's appointed Hokage and Naruto dies with a smile on his face having finally saved his best friend and accomplished his life long goal.