Does America have rockets to carry people to the moon today? Does America still have landers that can land on the moon and blast off for a return trip? If not, how difficult would it be to start from scratch?
Sorry, but I sure as sh*t would not want to be propelled into space and towards the moon in 45+ year old rusty antiques. The shuttles themselves already reached their age, those things from 1969 have long ended up useless and unsafe.
How difficult would it be to start from scratch?
Not hard at all. All the information and specs from the equipment and resources used to reach the moon are everywhere, including the internet. Money and interest is the main requirement.
Luck won't be required.
What's your basis for thinking that extinction is simply just another physical barrier to be overcome?
Experience and knowledge.
If humans can colonize and thrive on 3-4 planets at least, the chances of human extinction are reduced the zero..... the more planets, the more assurance of long term existence.
Let's say we humans live on 6 planets in the galaxy and doing well on each. If a major disaster on an extinction level occurred on one planet, humanity would live on elsewhere.
Let's say something catastrophic occurred and by freak accident two planet-wide disasters occurred almost at the same time as each other and prevented those planets from evacuating...... tragic, yet not an overall issue for humanity's long term existence.
Two planets doubles our odds.... more than that increases our overall long term survival by even more.
12 planets and extinction of humanity is more than squashed.
Even with 3-4 planets, if something happened to 1-2 planets, we still would have the knowledge of how to travel to other planets and colonize those, forever prolonging our existence before something happened to the remaining 1-2.
When a bird builds a nest in a tree to live and a forest fire occurs, they either fly off and make a new nest in another tree away from the fire, or sit there and wait to die in the burning tree.
You can sit in your tree and wait for the flames, I'd prefer to fly off somewhere else and continue to live.