If we look at Brood of Evil, Camilla enslaved and tortured Silas for his entire life to the point where his skull still sits in the basement, so it wouldn’t surprise me if Evie did the same.

I’d imagine they’d only get rid of a slave if they got bored of them or they got too old/broken to be fun to torture anymore. The only exception to this is Nancy, as part of the fun of torturing her is the catch and release. I can one day see Evie and Violet choosing to “retire” the detective bit and then just properly enslave her just like CG.

With Pam and the exchange student, Sleepy has hinted that Violet and Evie have plans to sell them off to one of their friends or a high bidder.

CG seems a bit different. It’s clear that Vi and Evie have some both fondness and hatred for her considering she’s their first permanent gimp girl and how she kicked Evie once and constantly tries to escape. I think they’re really turned on by her resistance to being broken, and every escape attempt only heightens their desire to torture her more.

I don’t ever see CG leaving their clutches. I think she stays for the rest of her life as a slave, maybe only being retired sexually when she gets too old and unattractive, in which case she will become more of a servant like Leopold. After that, I’d see Nancy replacing her as the new permanent gimp girl, Evie and Vi would frame it like they’re “settling down” and making a commitment to permanently enslaving her.

TL;DR: once a slave, always a slave, in one way or another.