But even if there's no backup, sometimes it's possible to recover file which updated/modified. I would recommend you to make raw copy of your drive (with tool such as HDD Raw Copy[1]), so later you could use recovery tools (such as PhotoRec[2] or Recuva[3]) without worry the data overwritten since you keep using it.
I'm not sure how Windows stores text files, but if it's really just stored as plain text, it would be quite easy to do a raw search for some of the known words on the entire disk.
Windows Notepad used to use ANSI format, but at some point (i don't remember when) it switched to UTF-8.