Blackbird isn’t on her nest tonight

We’ve got a blackbird that has returned three times this year to nest under our veranda, she’s very content with our household and we do everything to minimise traffic and noise under the veranda. She’s trusting with us and doesn’t spook easily. 

I’ve come home tonight and she isn’t on the nest, the three babies are fledglings, id say they’d be leaving the nest in the next few days however she still isn’t back at it’s pitch black outside. The fledglings are all tucked up sleeping but where is mum. I know blackbirds tend to come back to the nests at night as she has done every other night but where is she and if she doesn’t return what do I do? I can’t let them die