Called by the framework when Excel closes the XLL
virtual void OnXllClose( );
This function is called whenever a user unloads the add-in, whether using the Excel Tools - Add-ins dialog or indirectly, when closing Excel.
This is a good time to do any termination and cleanup that needs to follow any use of your add-in functions, particularly closing databases and logging off data feeds.
The default implementation of this function does nothing.