I've been waiting for this
The Sith should never return after the Emperor's death, because the Sith's way was completely and utterly destroyed by Anakin when he killed the Emperor. Now normally this would be a natural sith progression. Apprentice kills master for power/out of hate/etc. and becomes new master.
But Anakin didn't kill Sidious out of hatred or a lust for power, he did it to save the life of his son. It was a completely selfless act that goes against everything the Sith teach, and in that moment, the Sith died.