Is there any way to open an older version of a Notepad++ saved file without having the backup option enabled? I'm using Windows XP.
Not inherently possible, unless you had something external making it possible. For example a software which backups all changed versions of files.
Inherently, the best you could do if you never closed Notepad++ is keep pressing Undo (Ctrl+Z on english keyboards IIRC) until you're back at the state you wanted.