> Our primary and out-of-band network access was down Don't create circular dependencies.
With something as fundamental as the network, no way around it. - Okay, we'll set up a separate maintenance network in case we can't get to the regular network. - Wait, but we need a maintenance network for the maintenance network...
Two is One, One is None. There are absolutely ways around this, it's called redundancy. The marginal cost of laying an extra pair during physical plant installation is basically $0, which is why you'd never go "well we need a backup for the backup, so there's no point in having two pairs). Similarly, the marginal cost for having a second UPS and PDU in a rack is effectively $0 at scale, so nobody would argue this is unnecessary to deal with possible UPS failure or accidentally unplugging a cable.
In this case, there are likely several things that can be changes systemically to mitigate or prevent similar failures in the future, and I have every faith that Facebook's SRE team is capable of identifying and implementing those changes. There is no such thing as "no way around it", unless you're dealing with a law of physics.