Simple: You have to prepare for that eventuality beforehand. In some cases, it makes sense to configure VPN termination on the firewall protecting that link; in other cases, it makes more sense to build a VM that either natively or source-routes through that circuit and pokes a hole in the firewall allowing remote access. I generally do that with a Linux VM and allow ssh so that I can tunnel in quickly from wherever, including a friend's house after quickly downloading putty or using the native ssh in Mac OS X.
In some instances, I've even used GuruPlugs since they sip power and can easily provide a critical pivot without relying on anything but the connected switch. It's the best $100 you can spend in that case.
Having that emergency chute can mean the difference between being able to successfully troubleshoot a data connectivity problem with your carrier's support techs remotely and having to tell them you don't even know if your main firewall has power. In some cases, that lack of information will cause the carrier to require positive acknowledgement of firewall availability before they dispatch technicians to look for problems elsewhere along the circuit path, costing time and money.
Of course, if supplemental circuits aren't available for whatever reason, you should at least be able to get an analog phone line and dust off a few modems. It might be archaic, but even 33.6kbps beats 0kbps when you're trying to see what the heck just happened.
Also, take pains to ensure that your monitoring systems have sufficient safeguards in place to allow them to send email or SMS messages when problems occur. Tacking them all on a single mail relay isn't a great idea -- especially if that relay is external to the site. A better idea is to use local relays (maybe even that Linux VM) for this sole purpose and configure those relays to be able to send mail through several data paths.
Nothing is 100 percent foolproof. But tracing your remote access chain from your gear to your house and making it as stable and resilient as possible is far more Gallant than Goofus.
This story, "Stay connected when disaster strikes," was originally published at InfoWorld.com. Read more of Paul Venezia's The Deep End blog at InfoWorld.com. For the latest business technology news, follow InfoWorld.com on Twitter.