I don't use gears w/gmail and it sounds like that is what you are talking about, so I don't know specifically how it works but here goes anyway...
Find the Gears Sqlite database for your install. You will have to check the Gears docs for it's location on your OS.
Install the Sqlite Manager addon for Firefox if you don't already have something to open a Sqlite DB.
Fire it up and navigate to the location of the Gears Sqlite DB on your system, and open it.
Examine the tables and hopefully Gears has stashed your emails in there somewhere.
Not much but there you go. Good Luck!