If you're going to create a vacuum, that vacuum has to be replaced with something.
Spoken like the Mormon you are. Why does anyone have to replace one cult with another? How about reason, logic and facts ? That would be a good start.
If you ruin their faith entirely and don't replace it with something better, you can really screw them up emotionally.
Well, that is setting a low bar. You don't need to replace one religion with another. How about just seeing how it feels not to have someone telling you what to think, do and say? Why would it "screw someone up emotionally" to stop believing in ancient fables?
You can have that BORG mentality replaced by depression, plus you might lose any influence or relationship with her that you've established.
Assuming that leaving the Borg will make you depressed. It was an adjustment for me, but I was never depressed, I enjoyed the newfound freedom. Fifteen years out, I've never been happier.
Really Cold Steel, stop trolling for new recruits for your cult.