Earlier quoted context omitted.
Yes, same as the economy, too many things depend on infinite growth (retirement funds being the main one).
Retirement funds don’t strictly requiring that, they just require that there are more workers than pensioners — you could also sort that with a higher retirement age. (Long-Term question I’ve had: how does this compare with UBI, which is kinda like a pension but for everyone?)
That's not necessary. They require that the active workers (plus capital) are productive enough to keep life standards for everybody. There is not theoretical limit for how many workers are necessary. In the extreme it could be with one or zero workers.