This is a late response but this is something I remember asking for like two years ago, when Veneficia was initially released. She is able to negate the effects of the recall stone using her magical prowess, so clearly a method of disabling the recall stone exists and it surprises me other monster girls are just ignoring it. This is a great game but it's the first game with monster girls where all the girls share this odd code of ethics preventing them from enslaving the MC, when you would think many of them would love to have him as a pet with how sex-focused everything is and with how uncommon other male travelers seemingly are.
Threshold could do a lot with future characters or even current characters, who are intent on finding themselves a new slave. It's especially disappointing when you have that tengu, for example, stating she is going to take him home with her but then comes the recall stone, as a device which conveniently prevents the women from abducting him in his defeat, making that dialogue pointless. It doesn't even need to be this expansive enslavement system, just a bad-end whenever you lose to certain characters X amount of times.