Match Listbox Item To Column Entry

I have managed to set up a dynamic range called "Managers" which is held in a worksheet named "Lists" to validate entries in Col D of a worksheet named "PartTimeStaff" -

I also have 2 userforms which either add or delete managers names from the dynamic range, this all works well.

What I need to do when using the Delete form is to check that the managers name is not selected in any cell of Col D in the "PartTimeStaff" worksheet - this is to ensure the user has reassigned the records to another manager before deleting selected manager on ListBox1within this form.

The code which runs from a command button is below


Private Sub cmbDelete_Click()

Dim i As Integer
Dim SelectionsIndex() As String
Dim ArraySize As Integer
Dim RowToDelete As String

Application.ScreenUpdating = False

With Sheet2
.Visible = True
.Activate
End With

Set ManagerStartRng = Range("A3")

Application.EnableEvents = False

If MsgBox("Are you sure you want to delete this manager?" & vbCr & vbCr & _
"This action cannot be undone!", vbQuestion + vbYesNoCancel, "Confirm Delete") = vbYes Then