The Avatar cycle is probably going to continue.

[Kagerou]

Maybe part of Book 3, Korra will enter the Spirit World and try to regain the Avatar cycle, With Raava by her side it shouldn't be a problem.

I don't see why the creators would break their own series, So this is the only logical explanation.

 

[KingHashirama]

Probably in episode 14, called "Light in the dark". o-o