Just a topic for discussion. If Aang can take bending away from someone then it would be possible to put bending in someone. Hence Aang would have the ability to re-populate the air bender's.
Continuation of the story would be interesting. Zuko goes on the search for his mother. Azula escapes and becomes a rogue. The earth King comes back to rule the earth kingdom again indicates the source of all elemental forces came from the animals in which master that elements but indicate a book in the great library that was lost in a sand. They go with Toph to the desert to have her sense the location of the library and earth bend it back to the top.
The lion turtle said that before the bending of the element. There was the ability to bend one's internal energy. Therefore we can probably guess the the elemental bending skills were obtained by absorbing it from the primal animals.
