Yeah, with how she's trying to set up threesomes for him, is relying on him paying for her phones, and how her little sister is already attached to him, I can't see Chika giving Sensei up. Adding on losing her mother, her sick sister, how determined she is, and how desperate she seemed when she thought he was dumping her, she'll definitely either become the foundation of his Harem or she'll pull a Makoto, then find out she's not allowed to die and become the foundation of his Harem, anyway. There's no real way out of this for her, besides obedience.
I do wonder however, if her obsession with Niki might be a little damaged if they have a threesome. It'd be like meeting a virgin goddess you've worshipped for years, and she turns out to just be another human. Chika being an Admin to the Niki Simps group and how she rationalizes everything about her, shows she's not exactly seeing Niki in a healthy way at all. Instead of a sex god, Sensei might become the "evil god" who corrupted and defiled her goddess to the point that's she's unrecognizable, even to her most devout follower. Of course, Chika then might become a devout follower of that "evil god". Then again she might just rationalize that the Real Niki is just a lookalike. I'm definitely curious to see how it goes.