I have an asus router with a pi-hole on the network.
I was doing some work on my server and noticed that when pi-hole was down, I couldn’t access the internet. I was looking for some ideas online how to deal with this, but they said to have a second pihole on the network in case one is offline. Is that the only way to do it? Is there any way to have the network go back to normal if the pihole is offline?
No, that is not how DNS blocking works. It doesn’t just avoid responding, it responds but with a response that says that the domain does not exist or one that points to a different IP address.