I have never had in mind to mirror plain html pages. That would be an easy job, but also bad behaving. I thought of rsync access e.g. to the daily backup of the DB dump file and the uploaded files directory. So those that rely on access to the documentation have a chance to keep an up to date version local in their mediawiki. And I am sure that a lot of those people would put their mirror online in case of a long outage, if you ask them for it. I would. Even a slow access due to limited bandwidth is better than having nothing at all.