I'm not keen on a society dominated by resource exhaustion, grossly exceeded planetary boundaries leading to ecological overshoot and collapse and billions of early deaths due to climate change, pollution and conflict as everyone fights for whatever is left.

An againg society is a necessary step towards a sustainable population. Anything other than a sustainable population (number of people x consumption amount) will, by definition, not be sustained. A collapse will be chaotic and devastating. A managed descent of degrowth will have difficulties but could save humanity and the biosphere as we know it.

It's not as much a disaster as you seem to think.

Surely, you'd have a lot of people who are not in the active workforce. But due to automation + AI, we're going to see a mass layoff crisis in the next 10 years anyway, so if people retire, that's a good thing that young people can find workplaces.

Also it should be noted that large swaths of the population didn't participate in the economy back in the 19th century, when 1/3 of people was below 15 years of age. Still the world didn't end because of that, the opposite, that's when growth really set it. The lesson to learn here is that a large active workforce is not required to have a good economy.