I’m betting on deflation. Birthrates all support it.
Ah, demographics is history. China: from rags to riches to rags in three generations.
Check Islamic birthrates. That demographic is growing worldwide at 2%+ per year. Variation on Mohammed are the most common name in the UK. But European, US, Canadian, Australian, Chinese, Japanese, Korean, and Indian birthrates (ex-Islam) average about 1.4 per woman, where we need 2.1 to maintain level populations.
I foresee a bloody Asian war this half-century, with China and India allying and winning.
But we can have both declining birthrates and printing presses running 24/7. Since Socialist Insecurity is cashflow negative, this continues until the moral equivalent of Soylent Green approaches. Has happened before; travel the American Southwest to see Anasazi ruins of cities in the five to six-figure range.
What would the economic result of 1/3 the global population . . . or even 20% being relieved of breathing in this dimension?