Roosters have nothing to do with egg-laying.
Hens lay eggs no matter what.
If a hen doesn't mate with a rooster then the egg will just be an egg, and could never possibly be a baby chick. If a rooster mates with the hen, the egg the hen lays can be incubated or sat on, and it will hatch. Only when a rooster mates with a hen is there a baby chick in the egg the hen lays. Yes, the eggs that you buy at the store are not usually fertilized. Commerical poultry farmers keep the chickens in small wire cages usually with several other hens.