There are several possibilities as to what happened to the mom. A predator would be a likely candidate, but the neck would have been eaten such as the case of a coyote, fox, etc.

Another unethical probability is that your state wildlife officials had something to do with the swan's demise. Many states and federal wildlife officials are killing Mute Swans on the nest at night and stomping on the young or the eggs to ensure that they do not hatch.

These same public funded officials will misrepresent the Mute Swans to the public as being detrimental to the habitat, invasive and many other untrue attributes. In fact, the Mute Swans are beneficial as they are Sentinel/indicator species which alert scientists to problems in the environment such as the presence of heavy metals and harmful microorganisms.

The reason that the wildlife officials sneak in at night to kill the swans is because of the public uproar that killing the swans in the daytime has and continues to occur. The actual reason that Mute Swans are being killed by wildlife officials is to open wetland habitats so that they can replace the Mute Swans with the larger Trumpeter Swans for Trophy Waterfowl hunting purposes. So, governmental agencies are wiping out an entire species to support Trophy Waterfowl hunting which brings in more dollars for their coffers. Hopefully, this is not the case of your swans, but whether a predator or governmental wildlife officials, the remaining swan may not be safe and if he is scared, he may leave the area.

As far as the eggs, there is nothing you can do as the mother needs to incubate them for survival. If the eggs have been left in the nest for any significant amount of time, they have already gone bad and will explode into a smelly mess if you bring them in the house or try to incubate them. Unfortunately, this similar case is being played throughout the world during nesting/mating season when predators and wildlife officials are most prevalent. The Regal Swan