If I'm understanding things correctly .........
When Opalstack deployed a new DE IMAP server with empty mailboxes, would it have been a good idea if they had at the same time re-set the mailbox passwords?
All affected people would then be put to the bother of re-re-setting (or un-re-setting) their passwords;
but the subset of people who have "always on" IMAP Thunderbirds would have had the possibility, before re-connecting, of saving some emails which are now permanently lost.
These would be emails which arrived after the last Opalstack backup and before the last IMAP sync of their Thunderbird.
For such people, the only unavoidably lost emails would be the hopefully quite small number which arrived after their last IMAP sync and before the onset of the outage caused emails to start being held for later delivery.