I don't think it's cocky or 20/20 hindsight. Companies I've worked for specifically set up IRC in part because "our entire network is down, worldwide" can happen and you need a way to communicate.

I bet they never tested taking out their own DNS.

IRC does use DNS at least to get hostnames during connection. I'd be surprised if it didn't use it at other points.

I’ve setup hosts files in case DNS was down to access critical systems before. It’s a perfectly reasonable precaution.

My small org, maybe 50 ips/hosts we care about, maintain a hosts file stills, for those nodes public and internal names. It's in Git, spread around and we also have our fingers crossed.