This is a very interesting question posed. Especially in regards to my character Syd.
Syd's under a reincarnation curse. One of those incarnations was Darth Phyre.
For those of you who haven't read, Phyre was a horrific, bloodthirsty Sadist at least ten times worse than The Amalgam. She wasn't redeemed. But neither was she willingly converted to The Dark Side.
Instead, a faction of Jedi, after she had kicked virtually everybody else's ass trying to bring her down finally decided to just simply give her no choice in the matter and use magic to convert her against her will into a Light Side weapon, than had her unknowingly wipe out her own cult before imprisoning her essence in Nullification Resin.
The Point is, like Revan (Whom she was partly inspired by), Redemption was NOT Phyre's choice. Not at all. But nonetheless as Syd, she is heavily burdened by and horrified by her crimes as Darth Phyre, and deeply conflicted at the moment between helping Laertia, and trying to stop Starlin from going down her road, which she screwed up badly at Dantooine. After Sarka, she has begun to see it more Laertia's way, partly because she's in love, but mostly because Sarka traumatized her the way Nar Kreeta did with Laertia, and she's suddenly not so sure she wants the Order's idea of redemption anymore, given what she saw and felt in The Force at Sarka. But does she want to be Darth Phyre again? Certainly not. She is disgusted by and loathes the Sith version of her (Who really WAS the sort of vile, perverse monster that Jedi say all the Sith are). Many of her crimes are so horrific that Syd knows she'll never find real forgiveness. All she can do is pass on her teachings to someone she hopes will carry on whatever fragments of actual good that still live in Syd. Syd wants to be good, but she knows she'll probably never achieve that. The best she can hope for is to "Not be Phyre ever again."
This sentiment is clouded however, given her current actions, and she has grown as frustrated with the Jedi as Laertia has...so she is deeply confused about what she truly wants.
But one way or another, she is going to have a reckoning with her past through Laertia, whose parents she murdered and dismembered while still a Sith, and The Amalgam, who is Phyre's successor (and has a copy of Phyre's mind hiding inside said Successor)
I don't think she'll ever truly find redemption. The best that can happen is that she spends the rest of her life using the Light however she can and shunning giving into the Dark Side. But it is important to her to do as much good as she can, without expecting a reward, which motivates her fight with the Bryn'adul...she believes that by stopping them, she'll save more lives than Phyre stole.