Tsiolkovsky said it best. The earth is our womb, but we cannot stay there forever.

Extinction can ONLY be avoided by creating first an interplanetary and then interstellar settlements.

The rest is sheerest conjecture and likely as a snowball in hell. we get hit by a full ice age, that's the end. And it's coming.

Or a big asteroid, which we have neither the power nor the tech to divert, or block.

OR TN war which Putin is threatening now.

Get real. We get to the moon, set up manufacturing, self sustaining and growin habitats; and then we settle our system and then our spiral arm of the galaxy. It'd take about 25 yrs, well within the lives or most living today.