Dont think you understand how the force and balance works. There will always be sith and jedi even if one of them get all wiped out.The force wull draw in force user to each side, as in the will of the force of things.
Sidious did only bring the force out of balance, and Anakin got the force balanced again.
Balance is as easy as 50/50 you can say.And what you call dark jedi are the ones who turn into sith, dont you know the lore ? star wars cant work without the fight between light and dark.Other enemies for thee most part are just boring.
When did I say there would be no dark side?
My point was, there needs to be an enemy using the dark side of the force, and likely a red lightsaber. However, the dark side user(s) should be starting from scratch, just like Luke is doing with the light side. His "Jedi" are much different from the Jedi order of old.
The Sith line died out with Sidious and Vader. There will be baddies who will come up and fill the power vacuum, but they won't be genuine Sith.