This article will help you understand two things:
Deactivating a User: Removing someone as a user (taking away their login), but keeping them on the Directory so they can still be seen on the Accountability Chart.
Deleting a Person: Completely removing someone from your account so they no longer have a login and are not seen on the Directory.
What happens to the user's content?
All CURRENT/OPEN content will remain on the team that it is assigned to, and become unassigned so you can assign to another team member.
All ARCHIVED content will stay in the archive, still owned by the deleted/deactivated user.
Deactivate a User
Visit the Directory, click on the name, and click Deactivate User.
Delete a User
Visit the Directory, click on the name, and click Remove User.