If the heron isn't coming back they will come up eventually. But it takes some
time. I would not worry about them getting enough to eat.
I'll post the heron hints in case you've got a particularly determined heron:

Tips for herons, egrets and other fishing birds:
- bird netting over the pond
- put in an pond shock fence
- a motion activated sprinkler
(go to froogle.com to find these products)
- Migratory Bird Act forbids lethal methods,
heavy fines and jail time take away from pond time ;-)

good luck!
kathy :-)
A HREF="http://www.onceuponapond.com/"Once upon a pond/A