Option Explicit
Private Declare Function SetWindowPos Lib "user32" (ByVal hwnd As Long, ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long
Const HWND_TOPMOST = - 1 
Const HWND_NOTOPMOST = - 2 

Private Sub Workbook_BeforeClose(Cancel As Boolean)
    SetWindowPos Application.hwnd, HWND_NOTOPMOST,  0 ,  0 ,  0 ,  0 , vbNull
End Sub

Private Sub Workbook_Open()
    SetWindowPos Application.hwnd, HWND_TOPMOST,  0 ,  0 ,  0 ,  0 , vbNull
End Sub