I’m sure you have had this request before, but I have a suggestion for adding in a “release” thrall or pet from service by crafting a potion you place in their inventory which releases them from service.
This potion would only be craftable once you get the greater wheel of pain for thralls and the tier 3 pen for pets. It would be crafted in either a cauldron or an improved cauldron. It could even have a one to three minute expiration timer.
Once the thrall or pet is released from service they will become aggressive towards the releaser and must be eliminated. Or it could simply walk off into the sunset and fade away.
This would give us a way to rid ourselves of unwanted or lower tier thralls and pets when we can replace them with better ones or simply want less.