That's not quite right. The Sith in TSL were actually under the Exile's command durring Malachor V. Meaning, they were the jedi that resisted the dark side teachings from Revan. The Jedi at Malachor V were sent there to be killed, converted (to Revan's side, he hoped, or with the Exile severed from the Force, thus elimiating his inner threats. But Kreia, Nihilis, and Sion did not join ranks with the other Jedi converted. They became sith but did not participate in the Jedi Civil War. And, they didn't strike until after Revan came back as a Jedi to defeat his own Empire, then went into the Unknown Regions to pursue the True Sith that came back for The Old Republic MMO.
After he was away, T3-M4 returned to known space without Revan seeking out the exile even though, Revan was not sure if she would forgive him for his attempt to kill her, earlier. The exile eventually does forgive him, and goes into the Unknown Regions after learning from Kreia where he was. She does not take her companions with her, just like Revan. Kotor III was supposed to be the finale of these having the two meet up, but since both canons had been set. You could no longer have four endings, when you knew Revan was light side male, and the Exile is light side female. We have, yet, to hear about what happened to them, but the True Sith empire does return to know space for The Old Republic, so it's more than likely they failed to destroy the Empire, even though they would have made a dent, I'm sure.
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