Odds of Hanging On
The basic concept of an elevator hasn't changed all that much since its invention. Sure, the technology has gotten a little more complicated, allowing for better safety features and express cars that serve certain sections of high-rise buildings, but the core idea remains the same.
Therefore, if you're willing to continue learning and adapting to whatever new technology comes along, you've got a pretty good shot at keeping your job for as long as you want it.
Plus, the trend of more people moving to urban areas means more construction of buildings tall enough to warrant elevators. So we don't think you should worry too much.