Countries and institutions should always produce things where they are excellent at producing, in forms of specialization and compete in terms of comparative advantages.
- China weaponizing the world's dependence on rare earth
- The US weaponizing the world's dependence on SWIFT
- Russia weaponizing Europe's dependence on natural gas
- Iran weaponizing the the world's dependence of oil supply through strait of Hormuz
China could have the monopoly of rare earth production and refinery for all of eternity. But because of their reaction towards all the us allies when the us increased tariffs, I don't expect them to be relevant enough to disrupt markets with rare earths sanctions in 10-20 years.
... Except when they can't in any meaningful span of time.
You don't have to replace 100% of workforce, replace just the ones whose work is the easiest to do by a robot.
Replacing 50% of workforce buys you enough time that by the time your available worker pool has shrunk 50%, robotics and AI will be much better and you will be able to replace another big chunk.
Production-wise, shrinking demographics are not such a big deal (they still have a lot of youth unemployment).
Shrinking demographics is a problem due to a) the ratio of workers vs seniors, b) shrinking overall demand pool -> shrinking economy c) smaller overall talent pool -> less diversity, less 'geniuses', i.e. the real drivers of innovation, and less capability to mobilize for great projects