if it vanished there'd be a load of work to do
So I assume you have a contingency plan ready to go?
All this CI/CD stuff is supposed to deliver reliable, scalable and constantly-evolving business-critical services. That its foundations* are quite so precarious is... ironic. Let's go with ironic.
*of which Docker Hub is merely one - we're looking at a whole ecosystem of potential fail in the dark depths protected by impenetrable acronyms.