My favourite web site is up again.
It was being moved to a different host, and it takes 24-48 hours for the DNS change to propagate.
What one ought to do in this situation, is have the site in both places for a couple of days. That means that the "old site" has to be locked for updates, because if anyone posts a comment to it, that will not be on the new site, so will seem to vanish. But maybe there wasn't any way to temporarily disable comments.