Brine shrimp all dead! So much for live fish food?!?

I bought brine shrimp to feed my fish - and the whole tank seemed to love chasing after the live food. The actual life of the food, however, didn't seem to last very long. Is it still a treat to feed fish dead brine shrimp? Or should I just throw them out? How long should a brine shrimp batch last (how long should they live, and how long until I should throw out a jar of them)? I thought the whole point of these critters was that they were alive!!