They should be fine. Just get them warmed back up & continue on. I just hatched 3 batches in a staggered hatch that lost power at leadt 4 times & got to 55°F or lower at least twice.
X's 2! Don't throw them out. The are fine. They are pretty much grown, just absorbing the blood and yolk. You may have a later hatch, but they should hatch!