Typically when this occurs in CS5, the auto recovery function will kick in the next time you open the program up
The word [Recovered] appears after the filename in the title bar of the document window to indicate that the document contains unsaved changes that were automatically recovered.
If you cannot see them, Illustrator creates temporary filesending in " .tmp " for example photoshop files would be: ~PST#####.tmp in Windows; or Temp##### in Mac.... (### is series of numbers)
Those files are temporarily stored in the hard drive and deleted once you save the file or close the program BUT if the program or computer crashes sometime they stay.
If the file got deleted or corrupted then you will not get this file back again.
Search your system for TEMP followed by numbers as shown above and see if you can find it.
Non-commercial source- http://www.filerepairforum.com/forum/adobe/adobe-aa/illustrator/383-%E2%80%8Bcorrupted-fonts-in-illustrator-file-urgent-help-need
Free-to-try Illustrator Repair Kit
is available on: -