For the soil to break down and create compost it has to be damp for the worms and bacteria to be able to exist. As Mozcat said; once the worms have been through the top layers if you don't add more then they will go down to the bottom of the compost. Just water the compost with a watering can if it gets too dry and make sure that you add new vegetation or coffee grounds, tea leaves (not the bags though), apples and egg shells. They will soon come back.
I have some pet worms that I keep in a covered bucket in the basement. I change the compost every four or five weeks and add powdered milk and coffee grounds to feed them. All the old compost and the smaller worms go on the veg' plot and get mixed into the soil. I will be taking some of the larger worms from the bucket for a day out on the river bank tomorrow. Some will be going for a swim.