When selected value not existed in a dropdownlist

Hello everyone, I have a situation like this:
<cc1:MyDropdownList ID="ddlWorkArea" runat="server" > </cc1:MyDropdownList> <cc1:MyDropdownList ID="ddlEmployee" runat="server"> </cc1:MyDropdownList> They are cascading dropdownlists. Select a work area from the dropdown and it populate the employee dropdownlist who are still working for the company. Here is stored procedure to populate employee dropdownlist:
Select employee_id, employee_name from Employee_Table where active =1 AND work_area_id=@work_area_id Now the management team create a document for an employee and here is the table in my database
Document_table has two columns (for example)
document_id, employee_id
1                        2
2       &n ...