OP - MInthara is Evul! and will not care for you if you don't kill the Tieflings. She will kill YOU.
That's true of True Soul Minthara. Once she's free of her tadpole, she's a much more practical brand of evil, and calls you out for killing the tieflings (unless you had a good reason for doing so). While it makes sense that Act 1 Minthara wouldn't want anything to do with you unless you exterminate the Tieflings (hence no goblin party and no Act 1 romance), Act 2-3 Minthara is motivated by her oath of vengeance against Orin and the Cult of the Absolute. If anything she should be MORE motivated to join you if you've been in opposition to the cult up to that point.
