There's a lot of problems societally that happen when you go below replacement rate that are probably not being accounted for in that simulation. For example, t

There's a lot of problems societally that happen when you go below replacement rate that are probably not being accounted for in that simulation. For example, the age proportionality can become massively fucked with populations that have a massive majority in retirement-aged people and people under working ages leading to extremely low working-age people. That type of collapse can also accelerate unpredictably since we don't have exact ideas on whether or not there is a "catastrophic threshold" that replacement rates can go under.