Mostly this should be a non-event due to renewal long before expiration? Although huge deal I suppose for services that require issuing new certifications constantly; Let's Encrypt would be major failure mode for them.

As they move to shorter-lifetime certs (6 days now https://letsencrypt.org/2025/01/16/6-day-and-ip-certs/?utm_s...) this puts it in the realm of possibility that an incident could impact long-running services.