Duck Seems to Have Deserted Nest?

We have a duck nest in our backyard and it seemed like the mama duck started incubating because she was sitting on the nest all day for two days. Unfortunately on the morning of the third day she was no where to be found and there was a broken egg around the nest. It has been almost two full days since we found the egg shells and still no sign of mama duck. What do we do? Can we save the ducklings?