Do you have another hive you can borrow some brood and bees from? If so, and the other hive is strong enough, take a couple. If not, this is a good example of why it's better to have two hives than one.
Are there enough bees to cover the brood? If not, the brood is likely already dead, but you could TRY sealing off the hive with some screen, putting in a patty and some syrup, then incubating the hive by putting it someplace with a heater that can keep it at around 95-100 degrees Farenheit for anywhere from 3 days to a week or so. It would be a long shot though, and most likely you won't be able to save them if that's the case.
If there are enough bees to cover the brood, then feed them with the patty and syrup and screen off the hive for 2-3 days max, then open it but leave a robber screen on it, maybe even move the hive some distance away and monitor the situation; if further robbing takes place, screen it off again for slightly longer... lather, rinse, repeat.
That's what I would do anyway, others might have better tips for you. Good luck with it.