There is plenty of oxygen in there to sustain the chick for a good while. Keep the incubator CLOSED, so it does not cool down or dry out the air, and get the electricity going again as soon as you get a chance. Don't cover the incubator with a blanket or anything, it needs the air holes to stay unobstructed so some air can still get in and out (passively)
Do not open it if it just hatched out.
It takes a brooder a while to totally cool down after no power.
I had power out during incubating and did not open it. The chicks where fine. Get it back on as soon as possible.
Some people if it takes a while put a blanket to keep it warm but i never have done that.