What part was the accident, copying files from multiple folders without also copying the folders? Or Moving instead of Copying?
I'm trying to figure out the logic of intentionally copying everything to a single folder. If you ever did need to "restore" from that backup, you'd be faced with exactly the same kind of problem you have now - the need to re-organize images that you spent who knows how many hours organizing. Why didn't you copy the folders as well as the images?
If your folders were organized by file date, then it won't be horribly difficult to sort them by date and move them into separate folders again. If your folders were organized in some other manner (topic, location, client, etc.), then let's hope you embedded those criteria into the image files' metadata. If so, there are programs that can search and sort those files by metadata criteria.