With the EA add-in model, it is possible to react to the user closing down EA by clicking on the 'close' button.
An EA_FileClose event is triggered, and in response to that an add-in could for example show a message box asking if the user 'really wants to close'. If the users chooses accordingly, is it possible to cancel the closing down of EA somehow while handling the EA_FileClose event?
No. You could re-open the file. A bit silly, indeed. Maybe you raise a feature request. But don't hold your breath...