Taking off the tech hat...others have given good advice for triage on the equipment, etc.
Safety of you and your staff is the priority. Anybody who does not need to be there should get to safety now, before the evacuation order comes. The fewer people to be accounted for, the less chaos there will be if you need to leave on short notice. Make sure to exchange cell phone numbers (if you haven't already), so you can rendezvous with the others later on.
Assign a person to be the safety monitor--to stay at the phone and radio, and get the word out to all others if the evacuation order comes. Vigilance is their only assignment. The safety monitor should have a list of everybody still on site, to be sure nobody is left behind. If you get the call to evacuate, you'll have only minutes to get everybody out and down the road to safety.
Have N+1 vehicles ready to go, where N is the number you need to get everybody to safety. If one doesn't start, don't mess with it--leave it behind and call the insurance company later.
You should have two ways out. If one becomes impassible because of the fire, head down the other way immediately.
I hope you and your center escape the fire. But if it comes to a choice between you and the data center, let the servers melt!