Hi,
That same option already affects the files of the products the same way it affects the images.
So what you're talking about should already be there.
Moreover, the delete function for the files and the images uses the exact same function called deleteFiles in the file administrator/components/com_hikashop/classes/file.php
So since it already works for the images, I don't see why it wouldn't work for the files.
Note that I'm talking about the files that you can upload in the "Images & file" area of the products. This doesn't apply for images and files uploaded through custom fields.