Question: are there any sith purebloods left?
Answer: Actual pureblood sith haven't existed for millennia, since the years after the dark Jedi landed on Korriban and interbred with them. After a couple centuries, pureblood sith no longer existed. ... So while there may be sith left in small pockets, they won't pose a threat to any civilization for thousands of years, if ever.