Some fans speculate that the air-benders weren’t all gone, however, as we only see definitive proof of one battle in one air temple -the Southern Air Temple. An attack on the Northern Air Temple is also implied, though we don’t see any proof that the Fire Nation made it there before the Mechanist occupied it with his people. The Western air temple, in comparison, is practically undamaged when Aang arrives there, suggesting that the Fire Nation didn’t attack all the air temples. The theory also makes sense because air nomads were not settled people like other nations, so there’s a good chance some of them remained alive and in hiding.

One theory says that it’s because Aang was never supposed to be the Avatar in the show’s timeline. His preservation delayed his demise, and it was actually Katara who was set to be the new Avatar, as Aang should have been long gone by then. Why Katara and not anyone else? According to the Avatar cycle, an air-bending Avatar is always followed by a water-bending one, and Katara seems to have been the most gifted water-bender around. If it’s true, that would mean Korra would have never been the Avatar if Aang hadn’t messed up the whole thing.