You can easily remove employees who have left your organization by deleting them in the Users menu. Once you've removed an employee from your PeopleGoal account they'll no longer be able to log in or access their profile. Any items that they had created will remain open in the apps, because other users may interact with these items going forward - for example, if a manager leaves your business, their direct report will still want to see their own performance review and view the manager assessment given by the manager who has left.
To delete a user:
Once you've deleted an employee you'll only be able to restore their profile by adding their user profile again or sending an invitation to their email address to re-join the account.