I don't know if this will have a huge effect. First, China tends to try and keep people employed even if they're economically unproductive, in places like state enterprises. That means there's a lot of slack, a lot of jobs that could get cut without causing any adverse effects. Second, the trend towards roboticization of production lines is accelerating, is wiping out whole categories of jobs, and the robots themselves are often 'Made In China'. If you go on AliExpress and look at anything from pneumatics, to hydraulics, to electronics, to complete machines for doing stuff like packaging, you'll see it's all available domestically at a bargain basement price. All of these things increase worker productivity. If Chinese factories hit the level of automation you get in US factories, then it won't matter that the workforce is tiny and it's supporting a ton of old people.

Way to many people work on filler jobs that will go away and automation will also solve a lot of the problems. China has about 22% people working in agriculture, that will go down a lot over next two decades.

I wouldn't count on that. Sure, you can see increased productivity through farm automation, but that assumes that the farmer can afford said tools. Those that can might be able to grow more crops on less land, but they might be too preoccupied with paying the farm loan to go around buying-out their neighbors.

farmes are almost untochable, like in india but without voting power. nobody want 22% of its uneducated population making trouble in the cities. Hukou aka stict residential permits almost serve that purpouse

Would that mean the population then will be much wealthier (as happened after the Black Plague)?

Unknown. It's never been tried in an industrialized nation. I have a feeling it could easily go the other way and return China to poverty with not enough people to sustain their current economic output. That depends a lot on what's possible to do with automation. It could also have drastic effects on the knowledge sector, breaking down chains of training and knowledge transfer. A lot of expertise could be lost.

If you want to see the results of a fully industrialized area losing over half its population look at urban Detroit.

probably the opposite.

In the black plague, most of the wealth was durable physical assets like land, tools, farmhouses, ect.

In modern economies, wealth usually buys services and consumables. Less cheap labor will be a big hit to these costs. To make things worse, the workers will have to financially support a large aging population with a shrinking young demographic.

It depends on how you measure it and how it happens, but if each couple has one kid, and that kid inherits from both parents, after awhile the kids are inheriting a decent amount.

Or, all the excess "wealth" could be sucked up by the government/companies/large land-holders and everyone else stay roughly the same.

The End of The World Is Just The Beginning delves pretty deep into this. Very interesting read.

Don’t think so. This isn’t a case of population declining because of a one off event, killing off the old and infirm first and leaving behind a (relatively) healthier population.

This is more of a gradual decline AND ageing. The decline isn’t happening because the old are going away; its happening because there are too few young people being born.

That just leads to stasis. Nothing wrong with that, but it completely messes with all our current economic and governance models

Definitely. Unprecedented in human history. Wide-ranging social, cultural and economic impacts.

What's unprecedented is the insane population explosion of the last ~100 years. It's only good to have major reduction to saner levels.

Yes, but not before a lot of pain. All our current economic models are built on population growth.

Slow growth essentially means that the population pyramid becomes too top heavy. You’re going to have trouble if your country is filled with 70 year old pensioners and the trickle of tax paying 20-40 year olds slows down.