My only concern with this method is saving an unwanted change
I click to close a file expecting to see the save dialoge I can say no to and re-open the file and start off before I made the last changes.
One of the macros I use deletes a sheet, if I run that accidently I can't go back,
so I close and re-open not saving the mess-up.
-I'm re-thinking the reason for the post out loud bear with me...

(case 1) - I think if the file can test if it has been saved, then updating the hidden sheets, re-saving and closing with-out prompt will be good.
(case 2) - if it tests not saved, we should prompt to save and then update the hidden sheets on close.
(case 3) - If the file tests not saved and the user declines save we should close without save or altering anything.