Make them sign a contract where cover gets a life time permission to use the talent's voice with the help of AI and other sofware.

Make the talent record a lot of voice samples during their work time.

After a talent retires, all cover has to do is boot up the AI version of said talent, this way they can still milk on their image.

The vtuber can still show up here and there with their AI version.

This way no holomem will ever graduate anymore.