You can't. Once you close Maya the history is erased.
Get in the habit of creating multiple saves. For instance:
save1.ma
save2.ma
save3.ma
save4.ma
etc.
That way you always have something to go back to in case the latest file gets corrupted or you do something you shouldn't have done.
Dave Baer
Professor of Digital Arts
Digital Media Arts College
Boca Raton, Florida
dbaer@dmac.edu