Why does the employee no longer appear in the list?
Employees: create an Employee in order to assign to an Activity such as completing a new application, or performing a service so to receive a commission.
From the main menu bar choose the Settings-tab, Employees list, click on the bolded Last Name and then you will be able to either edit attributes for the Employee or Delete the employee-account altogether.
Be sure the Expiration Date has a date well into the future or it will not appear in any selection drop-down list.