I have 5 hens that never started laying again. It has been about six months now. Our local law says that if I catch the dog in the act I can kill it as long as it dies on my property. I sent messages to all the neighbors and have not had a dog in my yard since. I am starting over with 20 new chicks Monday. Neighbors dogs have killed 15 in the last 1 1/2 years.
edit: I have three acres and the chickens are seldom free ranged anymore.
Mine took four months off after an attack. Give them some time to heal then start trying to encourage laying. Use a light in the coop to simulate longer days and feed good treats with protein. Put a fake egg in the nesting boxes and just have patience. good luck!