Interesting, thank you all for the replies. I would have a hard time considering Bane to be someone who has left the Sith Order, if anything I would classify his actions as a hostile takeover/reformation of the Order. Now that Sinrebirth brought up Ventress and her actions, which I really haven't been following as I don't watch The Clone Wars, that is very close to what I am looking for. Though I don't know if she could ever have been considered a true Sith, if I remember correctly she was really just a fallen Jedi who became a Dark Jedi who was fortunate enough to have received attention and training from a Sith. Unfortunately as she never was formally accepted or into the Sith Order she doesn't count, granted this is just a technicality but still. Millenial however seems to fit the criteria of what I am looking for, and as I haven't read anything about him prior to hearing about him now I will go and do some research. Thank you for the information.