There's no one answer to this question. It depends on too many things.
I could say that if you want to know how viable a hen is over a particular period then it depends on the breed.
ISA Browns for example are great for the first season which is why they were bred for battery use. They tend to either die or become ill early in their lives due to the egg laying pressure on them. There are exceptions in that breed too. If they live on, the second year normally has around 50% less production (or so).
Heritage breeds tend not to lay as heavily in their first season, and have longer rest periods when moulting or if they go clucky. These breeds will lay well enough over a 4 year period and then fall off after that (but there are exceptions).
The toy breeds (like Silkies etc.) Never lay heavily anyway.
You can also bring feeding into the equation. Those people feeding intensively can extract a lot more eggs than those simply feeding pellets and table scraps. There are a lot of factors at play here.
I hope this helps and brings further comment from other board readers.