There is the story that one dies within seven days when one becomes enlightened as an unordained person.
I heard as well that one dies that very same day one becomes enlightened as a layperson. Which would make sense, taking the extinguishment of the "self" or "I" as meant as the dead.
For an enlightened being there would probably not be much left to do as a lay person in this world. It would not make sense to live on in lay life.
I remember the story of on recluse, Bahiya, the bark wearer, he received a brief teaching from the Buddha and became enlightened, within the next hour or so he died. The Buddha and some monks came across the dead body and the Buddha said, >Monks, take Bahiya"s body, put it on a litter, carry it away and burn it and build a stupa for him. Your companion in the holy life has died.< translation from John D. Ireland
So the Buddha seem to have regarded Bahiya as a Bhikkhu, so to say, because he had understood.