I lose power more often than I would like, for times when I know it's going to be out for a longer period of time I have a generator. But, I will shut off the lights, as well as one of the heaters and just alternate which filter is running.
In the past, I had about a 3-day power outage and not a large enough generator. Everything was off in the tank, in that case, I wrapped it in blankets and hoped for the best. Thankfully despite the water being really cold when the power came back on, I don't believe I lose a single fish. In all honesty I expected to find most of them dead, but nope, even GBR's I had at the time survived the cold.
I believe you can get battery powered air pumps, I may pick up a couple of those to run sponge filters on as well to help in any future power outages.