If your letter was saved on a drive and you're using Windows 7 or later, you can go to My Computer and right click on the respective drive and select Restore previous versions.
If this is not working for your, then you need to go to Tools> Options> OOo> Paths and browse the temporary folder. Once you reach that folder, copy all the files and change their extension to ODT or DOC and chances are the file will open with your content.