You can use "terminate" event,
example, your FormName : UserForm1
write this program on terminate event :
Private Sub UserForm_Terminate()
UserForm1.Show
End Sub
even user click the X on the very right of header, userform1 is still show up.
for the "END"/exit button, example : commandButton1,
Private Sub CommandButton1_Click()
End
End Sub
Now, we can force user by using CommandButton1 to exit !