If your router allows it you can set your gateway IP from the router (i.e. 192.168.1.1) as the second DNS address in the DHCP settings. So your routers DNS settings would then act as fail over in case your pi-hole is down. That’s at least how I have done it on my ISP router.
It’s just that we as humans need someone we can blame for our misfortune. Which gets complicated with an artificial intelligence or even simpler algorithms behind the wheel. There’s no-one in particular you can scream at.