They should be on your backup. Most people make such. You don't? Then look in the recycle bin.

Or maybe the files still are there but some setting has changed in WLM, so it looks in the wrong place. Did you check that setting already?

http://email.about.com/od/livemaildesktoptips/qt/Identify_Your_Windows_Mail_Live_Mail_or_OE_Store_Folder.htm tells how to find the current setting.
You might find http://www.emailquestions.com/windows-live-mail/2487-backup-windows-live-mail-2011-a.html useful also.

Kees