In this scenario the galera DB is only hosting virtual aliases/account info etc -- it's essentially read-only unless I'm adding accounts so the fail cases are less severe than if I was constantly writing data.

I'll add a section on recovery, but even with a few hundred thousand email inboxes my database size is likely to be under 100mb and backing that up will cause no issues in live since I'm only doing SELECT 99.99% of the time; each of my nodes dumps the db into /var somewhere every hour.