[elcomet]

What if your CA is down for a day? Imagine let's encrypt being down for 24 hours and all if it's certificates going invalid. That would be millions of websites unavailable..

[josephcsible]

This is no different than an OCSP server going down for a day. Either the site becomes unreachable, or clients take a risk by accepting a certificate that might be revoked.

[Avamander]

When OCSP is down nothing happens with most browsers. Except-Staple might worsen it a bit, but how many use that?

[josephcsible]

My point is that connecting with OCSP down carries the exact same risk that accepting an expired certificate does. In both cases, the risk is that the certificate might have been revoked without you knowing it.