When editing Keywords in the Site Collection Administration - there is a field for a 'Contact' who should be alerted when a keyword expires. There is another field for 'Review Date' with the text " The Review Date box, type the date you want this keyword to be reviewed by the contact."
I am under the assumption that if the Contact person is valid and the Review date is set, an alert is sent to the contact to review the keyword.
I cannot locate any documentation as to how this review process is designed to work.
Screenshot below -
Jan Headrick