Unbeknownst to many people, but knowst to us (Spaceballs movie reference), Dropbox does keep file versions.
"Dropbox is like a time machine. It keeps snapshots of every change in your Dropbox folder over the last 30 days (or longer with the Packrat feature). So even if you saved a bad change, or if the file has been damaged or deleted, you can restore the file to an older version with only a few clicks."