When I play my sith characters i tend to do more evil things. However part of the sith code is to never dispose of a potential ally (not specifically stated in the code but is explained as an understanding in the sith warrior story). I they can be useful they live. My characters do not tolerate weakness and will not hesitate to eliminate a potential weakness to the empire. However if they have proven useful then they are an asset to the empire and to me.
And i did the same thing to that traitorous fool quinn lol. I enjoyed every second of that cutscene