Problem is you end up other places with the assumption thar it's never null. So in the future when you actually set it to null somewhere it will blow up.
People that assume that a (nullable) value is never null because the sample at hand does not contain a null value _will_ learn their lesson the hard way, the one you describe.
But even non-nullable does not always resist to time, I'd argue that use cases where the field _has_ to be null eventually emerges and somehow have to be mitigated. There is no easy solution to safely workaround that without either tons work that duplicates lots of things or taking risks by adapting the code base.
Every single one of us needs to wake the fuck up. The author is right that the planet itself will be fine without us. If we want to survive as a species, we can't bask in decadence and romanticize the decline.
And how do you plan to achieve that ? The denial of reality of human psychology and politics is one of the reasons denial of climate change is still rampant. Yelling at people with urgency only works that much, and it also amplifies resistance.
In the end, everyone needs to wake the fuck up implies a sheer resolution of the need for change, and you won't bring that by schooling people, yelling at them or even violence. The inevitable is there, do what you think is best, tell what you think is best and you'll probably have maximized your contribution already.
Contemplating how things plays out in the end is not nihilistic, it's a form of acceptance of the real hard truth about the grip we have, as individuals, on the mater.