As I mentioned last time, we have a tool to help you out if all of the people in your Team Foundation Administrators group are hiding out in an undisclosed location and you urgently need to perform some administration on your Team Foundation Server.
The tool, perhaps unsurprisingly, is "setup.exe". A user who is a machine administrator of the AT and DT machines (or just the ATDT machine for a single server install) can rerun setup and choose "Repair or Reinstall". This will add the current user to the Team Foundation Administrators group and the user specified on the service account page to the Service Accounts group (you can use the old one if you know its password, or pick a new one - then again, if you know the service account password, you can just use that to perform any administrative functions).
While this will take the server down for 5-10 minutes, that may be a small price to pay for getting someone administrative access. Of course, one of the potential mitigating factors is "don't have only one admin" and "don't let all of your admins go on vacation at once", but sometimes emergencies happen and it's good to have some workaround in a pinch.