Not so hard to predict. Society would collapse, such a gap in humanity would drastically impact services and the ability to maintain critical resources and infrastructure.
Think of the impact to medicine, labor force, productivity, economics. Elon Musk gets is, depopulation is the real issue.
The problem is real and having a tremendous impact on China. There simply are not enough young people to carry on and especially to support the large numbers of aging.
China has no solution to the delima and there is essentially no way out
https://news.yahoo.com/china-birth-rates-plummet-more-223414630.html