No. Unless you do something dumb like "don't test that the failover system is fully functional before taking the primary offline;" this applies to any maintenance, which also includes upgrades. Usual HA tactics apply - don't rely on one power source, one network link, or just about any SPOF. (Which means that requirements start breeding like rabbits, which gets expensive rather quickly - whereas Github is free-as-in-beer, which is good enough for most people)

Perhaps the only case breaking both at once would be deliberate action (DDoS etc.).