I don't think that any of the other birds will step forward at this stage. They've imprinted on the dead hen already, so even if one did, I don't think the chicks would respond. If it were me, I'd put them in a brooder and care for them until they could be integrated into the flock. Roosters will help co-parent with a hen, but it's doubtful he'd take over those duties since the hen is dead.
I've had hens die with no explainable reason too. It's sad, and I lost a favorite Cochin like that.
Great news (well sorta) it wasn't the momma-just checked and all is well, momma has her babies all snuggled in... Still sad I lost one of my girls, but so glad it wasn't momma. Since the babies arrived we've had so much rain and all the girls have been pissy pants so something was bound to happen!
A thread you might want to look in to is the "mama heating pad" thread by Blooie
Just in case you run into another situation like this again.
OOPS wrong link,
This should work better.