It's entirely possible that I'm missing something here, and I'm not sure if it's already been pointed out, but isn't everything that transpires after "The Guide" really just the product of poor decision-making skills on Korra's part? Consider: in "Beginnings" and "The Guide," we learn that Unalaq wants to open both portals to free Vaashu, become the dark avatar, start a reign of terror, ect., ect, but all of this is only possible if both portals are open. After he tries unsuccessfully to open the Northern Spirit Portal using waterbending, Unalaq is basically resigned to defeat until he learns that Korra is alive and in the Spirit World. Couldn't Korra could have avoided all this unpleasantness just by hiding out at one of the Air Temples until Harmonic Convergence was over? As long as the Northern Portal stays shut, Vaashu remains imprisoned and the world is safe for another 10,000 years, right?