We use an "emergency agent login ID". We have an agent built with a login ID of 8900911. The scripts have statements to change call routing based on this agent being logged in by a supervisor. We have a recording setup that basically says "due to circumstances beyond our control, the call center is currently closed. Please try your call again later". Once everything is back to normal, they log that agent out and call processing resumes as normal. Now this doesn't log all agents out, it just changes call routing.
FYI, we also have agents built with long login IDs for meeting agents, inclement weather agents, etc that play different recordings when they are logged in.
War Eagle!!