This is a terrific read. For investment purposes, demographic trends tend to play over longer time horizons than most consider.
Nevertheless, a country without immigration and with fertility rates below replacement will have a strong deflationary impulse, and it will grow. Perhaps until so many fiscal tricks cumulatively pile up as debt that cannot be serviced without currency debasement and high inflation. Perhaps Japan closest to this stage, which is still far off.
What is truly spooky is how many Western countries are on that path.