> In the morning, I resumed (?) the download, but HTTrack 
was 
> finished very quickly, and then proceeded to 'purge' 
> everything I had downloaded earlier!

Any errors in the logs?? This should only happend when 
links could not be detected, and will forcve the engine to 
match the current site (empty?)

> I still have the old.* files in the cache; is it possible 
> to re-create the deleted files from this?
Html data: yes ('continue an interrupted mirror') ; but NOT 
the images, and other binary data.