Recent evidence (possibly leaked) has pretty much confirmed the presence of another important, but familiar character in Avatar: The Legend of Korra.
The recently leaked ‘Legend of Korra‘ video clips have appeared to show us much more than Korra’s bending styles. We also saw an old water tribe lady that remorsefully talked about how Aang was no longer present, and how her brother along with the rest of her friends had all passed. Oh, and she has “hair loopies” too.
I think you can certainly take that as a confirmation that Katara will indeed be in ‘Legend of Korra‘. But my question to you is: how long will she stay alive?