completely deleting the account, force quitting Mail, power cycling the phone, launching mail and readding the account worked. It should be noted that in the middle of this process, the ALL mail tab showed mail from deleted accounts.
The IMAP accounts readded cleanly. Unfortunately, POP doesn't save read/unread state - it's an older, less featured protocol, so I had to manually make the phone mark 2200 emails as read. Fortunately, of my four accounts I use on the phone (I work on email server software for a living), that account had the least amount of email, the rest were 6k, 8k and more.
FWIW, I backed up and sync'd before upgrading to iOS7 and all mail was working fine for the year I've had the phone prior to the upgrade. It should also be note that I know several people that upgraded with no problems, some of them people I work with that probably have just as many emails and accounts as I do (if not more).