[livrem]

Lower population works if we can build better machines. In the best case it can work even for a retirement home country. It requires some political improvements to make sure the machines are employed in a way to make that possible of course.

[alkonaut]

So long as the demographics shifts are gentle enough it's also not a huge problem to have an aging or shrinking population. Higher efficiency will help maintain standard of living with an aging or shrinking population though. The only think important to not have an "end of retirement as we know it" is to not have wars, hyperinflatoin, or a complete demographic collapse (e.g. extremely low fertility rates for a generation).