It is highly unlikely that these eggs are viable. Once the female swan leaves the eggs for any significant length of time, they will freeze or get too hot, depending on the outside temperature. She will use her body heat and wet feathers to act as an incubator, only leaving the nest for very short times to bathe, eat and rest. Then, she will cover the eggs with leaves and nesting material to keep them warm/cool while she is gone. In this time, the male will usually only stand guard by the nest. Depending on individual swan and species, usually the male does not sit on the eggs or help with incubation. Again, this is totally an individual swan attribute for the males.

So, if the females is not sitting on the nest for a long period of time, the nesting material will not protect the eggs from extreme temperatures, heat or cold. It is for this reason, that it is unlikely that the swans even survived once the female died and ceased sitting on the eggs. The Regal Swan