When you try to delete a user you may receive the error message
The user is required by a participant.
It means that this user is the only member of a participant. As such, to avoid process execution issues, WorkflowGen prevents the deletion of this user.
On the user’s profile page, click the Activity report link on the top right of the form to see the list of the associated participants. You can check those participants (in active or archived processes) to replace the user with another one.