It's more a matter of whether or not the character is actually evil or simply "misunderstood".
If the character is evil, then a redemption arc is implied as character development. If the character is misunderstood, then the onus would be on the player to go through an arc of better understanding her perspective.
Evil characters do not need to pass the "arch of redemption" for "character development". Please, let's destroy this standard of erasing evil characters and their evil personalities. This is not a mandatory ritual for "character development".
I rly hope that characters like Minthara, Lae and Astarion will remain evil. And that they would rather cut MC throat than be kinder.