I had a 30 gal tank set up with 2 Gold Gouramis, 4 Black skirt tetras and an Emerald Cory whenever hurricane Katrina hit. I went back about 2 or 3 weeks to check on my stuff (no flooding luckily) and EVERY single fish was still alive, no filter or heater running. The water was crystal clear as well. If you think about it if they're not being fed at all then they wont produce any waste, therefore the water quality should stay fairly decent for a while. I heard fish can go a long time without food too.
In other words, if its just a short temporary loss of power ( a day or two maybe) I don't think theres anything to worry about. When the power does come back just to be safe you could feed them maybe once a day every other day, for a week or so.