What version of excel? And how did excel close?
If it's ex2002 and excel crashed, then maybe excel caught it. xl2002 has an
autorecovery (not autosave) option. The next time you open excel, it looks to
see if something extremely bad happened (crashes). If it finds that it did,
then you'll be prompted to save the last version of the recovery file.
Before xl2002, I think you're out of luck. (and with xl2002, if you just closed
without saving, it would be bad news, too.)