if you're seriously concerned about this, then the answer is to backup your notes periodically. There are a number of ways to do this - the one I use involves installing Evernote locally and then periodically exporting the database into Dropbox. Of course, this doesn't guarantee that your notes won't fall into the wrong hands. To avoid that you'd need to either encrypt your notes or run something yourself.
There is probably a diff history, so if the notes get out, encrypting only protects you on new notes going forward.