Ability to deactivate users rather than delete, and to sort by active, inactive and period of activation/deactivation

My user list (inside my company file) is full of people who have come & gone. Firstly, it is inconvenient when looking to see who is logged on; and secondly, time consuming when trying to match data entry in the audit trail to the relevant employee. I wouldn't always want to delete them, so that I can still match up my audit trail.