When I got my new 33.5KWh battery, it was the 2nd time I had a battery pulled from the car. The first time, the battery was "repaired" and put back in. I suspect that the determination to replace the battery depends on the issue.
I heard that a car manufacturer has to support a product for 10 years. Which I think is one reason the EV1 was scrapped and even the Chrysler Turbine car. Not exactly sure; just what I suspect. I'm not concerned about a replacement battery being available, but rather, a replacement battery being affordable. I suspect that by the time a replacement battery is needed, I'll either be done with the car (16 years old) or there will be someone or company around who can rebuild it.