Fortunately, most ACME clients, including my own, support other CAs as fallbacks. (Caddy's ACME stack falls back to ZeroSSL by default, automatically.)
That, and extended week-long outages are extremely unlikely.
That, and extended week-long outages are extremely unlikely.
You only need the outage to last for the window of [begin renewal attempts, expiration], not the entire 6d lifetime.
For example, with the 90d certs, I think cert-manager defaults to renewal at 30d out. Let's assume the same grace, of ~33% of the total life, for the 6d certs: that means renew at 2d out. So if an outage persisted for 2d, those certs would be at risk of expiring.