The expensive default is to leave a former employee on a full subscription because someone may need their files or mail later.
Start with the retention requirement, not the old job title. Microsoft and Google both provide ways to preserve former-user data without treating that person as an active worker—but the mechanics and feature boundaries differ.
Before changing anything, document who needs access, how long the data must remain searchable, whether legal hold applies, and whether the old address must continue receiving mail. Those four answers determine the right path.