It would only fail if the host hardware failed in a way that damaged all three discs, which seems unlikely. It's for data backup, not uptime redundancy.
Anyway, I don't fear the lightnings/storms/power surges where I am as much as I do the inevitable failures of the storage devices, or kernel bugs.
This is just a part of layered protection I have. Offline backups are nice, and I have them too, but they are out of sync all the time by definition. So unless absolutely needed, having a real-time synchronized replica is much more prefered.