Falling below subsistence means people starve and cease to exist until supply and demand equalize or “something else” happens. That’s what Smith was getting at. Thus subsistence is a price floor for human labor.

Something else could mean developing a new concept of ownership or a new form of redistribution.

I said that wages would fall below human subsistence level, not that income would fall below subsistence level. People would still get income from other sources such as investments, charity, and government (via taxes on others).