I'm seeing a steady raise to 10.9 billion people by 2100. And those are guesses. LOTS AND LOTS can change in 70 years, and will. Many countires are seeing a steady rise in middle class, so even if the population decreases a bit, there will still be plenty of comsumers. I don't see how less people automatically means declining everything else. Talking in absolutes like 'less people to make stuff' and 'not in a good way' is hyperbole at best. What stuff? Maybe things are no longer needed or needed for less time. Processes get more efficient, new tech is invented, more farm land due to rising temps, markets change, tastes change, people migrate, wars, famines, droughts, floods. Don't forget that there are tens/hundreds of millions of people that don't contribute a single thing to society from birth and are net leeches and drains and takers from the tax payers for 70+ years...bodies for the sake of bodies is not the answer.
Not to mention the advances in computing power and medicine could completely change the landscape in 20-30 years and an entire new crop of concerns, ideas, and issues arise...you never know.
We will adapt...we can see the issue coming, and the popuation will move on.....10.9 billion or 10.5 billion. Whatever.
Tearing down houses sounds like a great idea.....more open land for parks, wildlife, outdoor living, camping, hiking, maybe even cleaner air and water?! That sounds great for my future children!