You could simply check for the existence of the shortcut  in
the "DeskTopIcon" subroutine just before creating the shortcut by
enclosing the shortcut creation code  inside the if...then like this:

If Not Dir(MyShortcut) <> "" Then
With MyShortcut
.TargetPath = ActiveWorkbook.FullName
.Save
End With
Set WSHShell = Nothing
MsgBox "A shortcut has been placed on your desktop  for ' " &
_
ActiveWorkbook.Name & " '"
End If