We had to go away on Saturday/Sunday and we knew the babies were close to leaving the nest. They leaned way out of the nest and were interested in the world around. We just hoped they'd wait until we returned to leave so we could see and photograph it.
We returned Sunday and found an empty nest. Then I found 3 dead babies on the ground. We assume they left the nest and a cat got them. We wish we had been here to rescue them. Our yard is quieter than it has been for a month or more with no swallows around.
We hope for better luck next time round. And we've talked to our neighbor about keeping her cat out of our yard and she responded well.
So that's the end of the story.