There should be a WorkbookAfterClose event
there is a WorkbookBeforeClose event but there is no corresponding WorkbookAfterClose event.
Note that the WorkbookBeforeClose is cancelable so there is no guarantee that the workbook will actually be closed after that event is triggered.
Currently in order to get the WorkbookAfterClose event, a workaround needs to be implemented: https://exceptionalcode.wordpress.com/2010/02/11/how-to-get-an-excel-vsto-workbook-closed-event/
Harlan Grove commented
Picky: an AfterClose event handler couldn't be in the workbook.
Without VSTO, you could add Excel Application event handling in PERSONAL.XLS[MB], use its WorkbookBeforeClose event to schedule another macro to run using .OnTime and storing the workbook's FullName. That other macro would check whether the stored workbook's FullName were still open, and if not, does what it needs to.