When a Employee leaves you can choose to Disconnect that Employee. Go to Administration-Employee and Change. Select Disconnected under the option Status.
Active - Employees can see the organization, their projects and will be matched at the upcoming projects and roles.
Disconnected - The employee no longer has access to the company.
Preactive - The employee is connected to your comapny and can see Overview, create Resumes and update their Profile, but can´t see any Company Information. The Employee can be assigned to Roles.