My incubator dropped to 92 degrees for perhaps as much as a couple of hours. One pipped bird died just ready to hatch. They were due to hatch tomorrow. ARE THEY ALL DEAD????
If your eggs are almost fully developed to the point where they are now pipping and getting ready to hatch, a slightly low temp is not going to do them ANY harm now. Think about it. A few more hours, maybe a day, and they'll be hatched, and then you're going to put them in a brooder that's 90-95F, and immediately you'll be worrying about overheating them. Your dead chick was almost certainly not due to your slight temperature drop.