That happens sometimes. Don't give up on the eggs. Candle them and see if they are showing movement or growth before you dump them. You don't want to throw away viable chicks.
How far along are the eggs? My hen will sometimes be off the nest for an hour or so, and the same thing happened with her. I suspect another hen was in there part of the time because the eggs went on to hatch.
I go against the common knowledge and leave the broodies in the coop until the last few days. I have 2 of them due in a week, and I'll be moving them to the chick coop (I have a smaller, portable coop) over the weekend.
Good luck with the hatch.