About 10 years ago, I lost power for 4 days. I had a 90g mixed reef at the time.
I heated the house with my gas log fireplace, which also kept the tank warm enough. Every hour, I took a pitcher and scooped water out of my tank raised it up high and poured it into the tank, several times(at night, I would just get up once or twice to do this).
This seemed to work fine and I didn't loose anything. Of course, I didn't have any sps, only lps and softies.
I've also heard of people putting drops of peroxide every hour to add oxygen, but I have never had the guts to try that.
Today, I keep a couple of battery operated air bubblers and just hope any power outages(if they occur) don't last too long.