I love how you included that some people didn't make it. It was a huge change, and some people were "left behind" (died). Adaptations needed be made, and sometimes those are rough.
I wouldn't that much agree with that they (humanity as a whole) had forfeited, but instead adapted. It's what us humans have always been very good at - if not the best at. Cold? make clothes and wear them, ... We adapted to some of the most severe climates on the planet, and we live there (think extremely cold areas, and extremely hot, ....)... I would call this adaptation strength, instead of weakness, but I do understand your point of view. ^^ You also raised some existential questions, which I love very much. Very well done!

Thank you very much for your entry!