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Check in ~/Library/Mail and there should be a few folders and .mbox files. If so, there is all your mail stored in those folders and files.

could it have anything to do with getting rid of mobileme?

If you remove or cancel subscription, it shouldn't affect the syncing. If you delete messages on MobileMe, depending on how you sync, might remove in Mail.app.
 
Keychain Access>Preferences>Reset My Keychain then restart computer. Try launching Mail.app and enter in your password. If that doesn't work, you need to find the Mail folder (~\Library\) and move it to your desktop, you're going to have to "reset" Mail.app.
 
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