Is this what they call a "squish"?

Because when you are demoted, you are placed according to your skill rating.  You are not automatically placed in the next lower league.  

So, if you want to go back to Kyber, you have to finish the next season in Aurodium 1.  If you do, you will be bumped up in Kyber and, depending on your skill rating, you could be placed in K4 or even K3 if you have a really great 3v3 season.