I'm trying to bulletproof a spreadsheet template against being overwritten
by coworkers who must use it. I have set it up to force them to save it as
a normal Excel spreadsheet under a different name any time the template is
activated. All works fine unless I choose NOT to overwrite an existing
file.

To be clear, the saveas dialog appears and I choose a file name that already
exists. I am then asked if I wish to overwrite the file. If I say 'Yes'
everything goes fine. However, choosing 'No' or 'Cancel' results in an
error. How can I detect which button was chosen and handle the error?