If I understand you correctly, you managed to copy some of your POP email to "on my mac" but not all. At this point, if you can't get into mobileme (Apple gave a short amount of time after June 30 for users to make the switch - I assume mobileme is now down. If you don't have copies of all the POP/MobileMe emails elsewhere, I can't think of a thing you can do - I suspect it's now gone.
I am a bit confused by your reference to "IMAP", were you using some other IMAP account? Or were you using MobileMe's IMAP capabilities?
You haven't quite got my drift. I'm not in danger of losing any email - I have it all as a POP database, "On my Mac".
What I want to do is get that POP email history into iCloud. I thought I would have to do so by first converting it to IMAP in mobileme. But I didn't get that done before mobileme shut down.
Now how do I proceed?
Or, another approach to it - can I somehow transfer/convert my existing POP history directly to iCloud? (i.e. with first converting to IMAP).
Purchase Emailchemy, use it to convert your Entourage mail store to mbox, import the mbox into Mac Mail, then copy it to the iCloud account (i would suggest doing that in stages, it has to go up to the internet)