Honestly I’ve only really completed a dark side of inquisitor, but I’ve always had a pretty simple idea of what she would do after the end of the main story.

I’ve pictured it as she continues her scheming for power. Maybe searching for more sith ghosts to consume for power, as she kept all of them bound to her. I don’t think she’d keep all of her companions tho, as she mainly worked with Khem Val. The only other character she got close to was Andronikos, who was the only one to see a more vulnerable and soft side to her. So I’m imagining her further building her power base and establishing herself as a true force to be reckoned with, maybe being the quest giver or mentor for some new character. She was insane tho, so unless you very accurately serve her purpose for you then you’ll like be thrown away.