So sorry about all this happening! I had a bluebird pair one year in which the female laid four eggs and the male disappeared. He was gone for five full days and she stayed an incubated those eggs the whole time. I trained her to a mealworm feeder during this time. He did return on the 5th day and I am assuming it was her mate as he cared for the nestlings once they hatched too.
Also I have had a female return one year without a male and she laid eggs and half of them hatched and she raised them by herself. She was a bit of an oddball though, she was here for five years!
Good luck!!
Donna in WI