The economy in Britain improved after the black death wiped out half the population.

The black death didn't discriminate and wiped out people of all social statuses equally. It upset power balances rapidly.

Barring absolute chaos, people can generally plan for years and decades from now. Declining population is something we all know is coming. Those with wealth will, for the most part, hold onto it. Those born into wealth will, for the most part, hold onto it. Japan is always mentioned as the prime example of declining population in these threads, and while the population is declining and demand for labor is increasing, wages are not rising but poverty is. Maybe it'll change 10 or 20 years from now, but the trend is downwards for the average person.

That's true but I think which bit of the population remains matters.

The demographic impact of a plague is pretty much the exact opposite of economic flight. In a plague the fittest and healthiest survive and are unencumbered by the elderly and unfit, but in a demographic flight the fittest and healthiest leave. Similarly in a birth rate collapse the demographics shift towards the elderly and away from the young and fit.

That was under feudalism, not capitalism.

So change the economic system? The balls to the wall neoliberal, winner takes all, no safety net model that the Anglo American world has been moving towards for the past thirty years is not the only one. The Anglo American post war consensus model which was more redistributory correlated with higher growth rates (not saying it caused them, kinda hard to tell) while the Northern European corporatist, Scandinavian mixed model and Japanese corporatist models have all been successful in both creating economic growth and distributing that wealth more evenly amongst the population. It has always entertained me that the one thing that the average Marxist and neo liberal share is a belief that there is only one type of capitalism.

But neither the Northern European nor Japanese models can cope with negative real growth in consumption. Nor negative real growth in savings.

There is a fundamental issue in capitalism that there must always be growth. Without growth, the entire concept of investment breaks down and the business cycle cannot continue. You could totally replace it with something that isn't capitalism, but that's not a small endeavor and won't happen without massive conflict.

Our current reality is that if the population shrinks significantly, there is a good likelihood that will happen.