I have chickens and while the eggs are great, what you have is new pets that also happen to produce eggs as a side-effect. (Assuming you live in a city and not on a farm) You treat them like any other pet. Chickens will live 3-10 years. One of my chickens died a year or so after she stopped laying, another chicken is now 10 and lays one or two eggs a year but is otherwise looking as healthy as they day we got her. I suppose you could kill them or even try to eat them but most layers are pretty skinny and would not make a great meal.

They will keep producing their whole life. However, production drops way off after 3 years. My wife isn't keen on butchering or I would make soup with old hens. I have some freeloading birds right now that will get to live out their life while only giving me manure and an occasional egg. When they die they become compost.

I do keep dual purpose birds in the event that food supplies require a sacrifice to feed my family. It costs a little more to feed heavier hens but the security is worth it.