Where are you? mama can keep ducklings warm enough but I'd still make sure they have a house that will give them protection from elements and predators. if you want ducklings and the eggs are fertile just make sure again she has protection and good food and fresh water, if you don't want ducklings then by all means remove the eggs and dispose of them.
My ducks only go into their house at night, even in the coldest days with snow and ice they come outside. so as long as they have a place to sleep at night for protection they should be fine. just make sure they have water that isn't frozen solid, if you live where that may happen you might want to invest in a heated waterer, which you can get at TSC, I use a bucket and dog bowl. both have built in heating elements and only come on when the temp gets below freezing.