Good planning! Now, where does the IRC server live, and is it currently routable from the internet?
While normally I know the advice is "Don't plan for mistakes not to happen, it's impossible, murphy's law, plan for efficient recovery for mistakes"... when it comes to "literally our entire infrastructure is no longer routable from the internet", I'm not sure there's a great alternative to "don't let that happen. ever." And yet, here facebook is.
Also, are the users able to reach the server without DNS (i.e. are the IP addresse(s) involved static and communicated beforehand) and is the server itself able to function without DNS?
Routing is one thing which you can't do without (then you need to fallback to phone communications), but DNS is something that's quite probable to not work well in a major disaster.
While normally I know the advice is "Don't plan for mistakes not to happen, it's impossible, murphy's law, plan for efficient recovery for mistakes"... when it comes to "literally our entire infrastructure is no longer routable from the internet", I'm not sure there's a great alternative to "don't let that happen. ever." And yet, here facebook is.