I can't say for sure that this will work either, but when I run into issues like this, I just start toggling the settings - maybe set to show 500 messages then go back to mail and see if the download more messages comes back. Maybe turn the accounts off and then on again. I
could not get my email to load at all today - 4 different email accounts and all 4 seemed to shut down at once. I just kept turning mail off and on and restarted the device a couple of times and then it worked - all 4 accounts started loading mail again.
Sometimes, just restarting the iPad or resetting it can make things come back as well. Have you tried restarting or resetting? By resetting I mean hold the sleep and home buttons down until the Apple logo appears.