As an Admin, clicking into a user will give you the option to 'deactivate' them rather than delete the user from the platform completely. 

A deactivated user:

• Will still show in reporting features
• Cannot be assigned content
• Cannot be added to a group
• Cannot log on 
• Has all their permissions removed

If a user has been deactivated, you can choose to reactivate them however doing so will not reinstate any of their previous Groups or Permissions, these will need to be actioned again. 

A deactivated user will be hidden from a Manager's current direct report list. If the user is reactivated, the relationship will be re-instated without any action required.