How do I hide disabled agents and departments from admin dropdown menus when I don't want to delete them?

Disabled agents and locked departments will still appear in Admin Panel dropdowns -- there is no built-in option to hide them there. They will not appear in the Agent Panel dropdowns. Workaround: prefix the names of disabled/departed agents with a special wide character (e.g. a full-width 'Ａ') so they sort to the bottom of alphabetical lists. Alternatively, consider deleting agent accounts (ticket history is preserved) rather than just disabling them.