Considering all those things like regeneration technology and other technical stuff I think it may be better to avoid mentioning anything of that in the story in advance since it kinda takes away some of the fun as if devalues everything a lot. If something of that must happen just do it when necessary.

If there will be a sequel, I think the reason to do this again to another girl should be not the money but the fact that another girl is nymphomaniac who just can't stop masturbating and this is distracting her too much from studies. She always keeps running vibrator inside and her pussy is stretched a lot already to be almost useless. Getting rid of her cunt seems to be the perfect solution to this problem.