Between expansion and shrinking, their is this razor-thin third option, where you are perfectly breaking even. Which is impossible to achieve in practice, even if theoretically it looks like an option... any unanticipated event threatens to cause unplanned shrinkage. That needs to be repaired immediately, but there is no generalizable plan to expand back to the prior level and then stop immediately, far too easy to overshoot. These instabilities last for decades or centuries, and if another event happens before stabilization, they just continue forever.

Not expanding does risk extinction.