Get the generator or battery operated pump. Just have enough to run a powerhead, filter if you have one, and heater. If you can't get any of that, you would be best I think trying to fill up bottles with hot water and floating them in the tank to try and keep temp somewhat better.
I had this happen but I had a generator and it was only out for a few hours, good luck. Things like that really make you think about one of the battery operated pumps.