vCenter

How can HA work when the vcenter is down?

Instead I write down all, I would say Follow the below link. IF you still have some doubts I can explain.

How vSphere HA Works

Is this how it works when vcenter if offline or just how it works in general?

Even thought the vCenter is down its the HA agent who communicate to other HA agent installed on the other host to maintain the integrity of the HA cluster.

Also this HA agent have the state of  cluster configuration saved, therefore even the vCenter is down HA still works.

As mentioned in article through Network and Datastore heartbeat. Rest it will take decision to behave how you configured your Isolation response.

I hope this helps.

Okay see that there is an agent on each machine in the cluster and that there is a master and slaves. So why if you deselect the HA feature on the vcenter, it turns off HA and how is that any different than the vcenter server being down?

"Also this HA agent have the state of  cluster configuration saved, therefore even the vCenter is down HA still works" - I think this is the answer I was looking for that the configuration is saved on the hosts

But I would still like to know why it works when HA is deselected, does it remove the agent and the configuration?

That correct if you deselect the HA option in vCenter, I will remove the HA agent and HA configuration on host.

Please mark the answer as helpful, If you got all your answers.