That's the beauty of L&O. It doesn't have to end.
It does if NBC ever decides that it's sick of shelling out the money for it, which was the primary factor behind the most recent cast changes -- Sam Waterston had to take a pay cut and a reduced role, Linus Roache came cheap, et cetera. It's pretty costly to do all that on-location shooting, too. Considering that Law & Order
's ratings are still pretty comatose, I'll be stunned if the show is on the air two seasons from now.