I talked to a sales rep in one of their stores and they said the Roadster with the most mileage has 160K miles and the battery is still at 70% capacity. Not worthless but definitely less range.
160k miles isn't too much to sneeze at, and it's not unheard of for ICE cars to have 30% loss of power over that mileage. It still does hurt a bit thinking that you're buying a car with an expiration date built in, though.