Yeah, i mean, you're not forced to play with partners, so if you do whatever with them and keep on your way alone, the game will proceed normally, however you may have less quests and stuff as Sebille is also a character from the career and have her on story.
Btw, not sure if you'd consider this a spoiler or not but now that i'm in the middle of the act 3, i'd never ever consider killing her, Sebille changed and became pretty cute. lol
