Even the brightest minds don’t seem to be able to extrapolate their beliefs out to the logical conclusion that they’re describing a Ponzi scheme that will collapse eventually by definition.
However such a balance might be hard, it is difficult to see that interest in having children in advanced economies would recover as populations crash. In fact likely as there are less people around (and a greater proportion being old), child rearing becomes more expensive to the individual.
Note that economic growth is not necessarily predicated on population growth, it can also measure better use of the people we do have (hopefully in an actualization, more than an extractive, sense). People should be understood as a (in fact the most) valuable resource, not as a costly burden.