My DS warrior took off her collar, mostly because her being DS doesn't neccessarily equate to being bat-crap crazy into torture and mayhem. Then she told Vette, quite seriously, that removing the collar didn't mean she was free. So Vette stuck with her, mostly because she had nowhere to go without being dragged back and re-collared, there on the friggin' Imperial Fleet and then Dromund Kaas.
But ultimately Vette became pretty decent friends with my warrior, even admired her. Read above, about the not being bat-crap crazy into torture and mayhem bit. Being dark side doesn't mean you're absolutely nasty cruel and terrible mean, even. You just kill the people who need to be killed, after all.
You really like saying bat-crap, don't you.