I’m not picking on you but I will try to be honest to help you out for the next time you try this.
To answer your question, what time span are you talking about? How long ago did Mama stop trying the hatch the eggs and instead started taking care of her living chicks? When did they hatch, when did you move them, when did she stop sitting on the eggs? About how warm is it under the heat lamp?
Once the eggs get to a certain stage they generate a lot of heat themselves. They don’t necessarily have to be kept that warm from an external source. So it is possible the eggs may still be viable and an incubator may work. It’s not a specific temperature or time but more of a range. How late in the incubation makes a difference too. If you have an incubator, put the eggs in it and let them warm up for about a full day. Then candle the eggs to see what you can see. You may not be able to see much, especially if they have dark or colored egg shells. My dark green ones are close to impossible. But candle them to see if you can tell anything. Then candle them again in another three days or so to see if you can see any change. You might get lucky and see movement, but even if they are still developing you might not see movement but maybe you can see change.
Sniff the eggs each time you do this. If an egg starts to smell like a rotten egg get rid of it immediately, it’s not going to hatch and will only get worse. In this whole process you don’t know what is going on so try to be patient.
Since you said one had a week to go, it looks like you had a staggered hatch. That’s where the eggs are not all started at the same time. It takes an egg somewhere around 21 days from the time incubation starts until the chick hatches. That 21 days is not exact, a chick can hatch a couple of days early or late, but if they are all started at the same time they should hatch within a couple of days of each other. Since the chicks absorb the yolk before they hatch they can live for three or more days without food or water while the late ones hatch.
But if the eggs are not started at the same time the hen has a choice to make, does she take the first to hatch off the nest for food and water when they need it or does she stay on the nest to try to hatch the later ones and let the first die of thirst or starve. The unhatched chicks start chirping to Mama after internal pip so she knows more are on the way, but the first ones also start a certain chirp when they get thirsty or hungry. Most hens abandon the late hatchers to take care of the ones that made it.
So next time save up all the eggs you want her to hatch and start them at the same time. Mark them so you know which ones belong and check under her daily to remove any that don’t belong.
I don’t know what you mean by the temperature dropping drastically but broody hens have successfully hatched eggs and raised chicks even with the temperature below freezing a good part of the time. There are a few photos on here of a broody hen and her chicks out walking on snow. It is unlikely you needed to move the hen and eggs inside with a heat lamp with a normal hatch but with your staggered hatch it may have kept some of the eggs viable.
I don’t know when to tell you to toss the eggs if they don’t hatch. You’re traveling places I’ve never been. I did have a hen stay off her nest long enough for the eggs to fell really cold to the touch fairly late in her incubation, she went back to the wrong nest. I put her back on the right nest and she still hatched 11 out of 11 eggs so just because they feel cold doesn’t mean they are dead. To be honest I don’t have a lot of hope for those unhatched eggs, but I don’t know enough details to be sure. The best you can do is just try.
Good luck!
