I think with people like Savage, Ventrees, and now Maul, they are not necessarily looking to become Sith but... The rule of two of the Sith Order, is just a rule and as all rules, they can be broken. The only reason the rule of two exists is because it was decided the Sith became weak be too many drained the dark side powers. So any of those three could start following the ways of the Sith. Palpatine and Dooku would be forced to seek them out and destroy them (it's not like they can just sue them for illegally becoming Sith) and Dooku wants to do that anyhow because they have their personal grudges. Technically with Maul still being alive, there has been 3 sith after Dooku came along. I would have to believe, once a Sith, always a Sith but I am just guessing on that. I would have to believe it was Maul's use of the dark side in his hatred and urge for vengeance that helped him survive in the first place.