If Uther's soul was split and then the other piece was found maybe that's the end game for Sylvanas too. That perhaps we have been dealing with the dark/evil version of her soul and the good part is out there somewhere.
So. IF this is true. AND. IF she finds out that the jailer is holding that good part hostage all this time and turns on him (assuming she can)
Would you as a player consider that reason for redepemtion after all that's happened?