If their population dropped from 1b to 1m immediately, right now, then yes that would be a disaster. But imagine that their population falls slowly, as automat

If their population dropped from 1b to 1m immediately, right now, then yes that would be a disaster. But imagine that their population falls slowly, as automation increases their per-capita productivity. Imagine a future China with 1 million people, but the average person can produce 1,000x the economic value that the average person can today.