By definition, the United States as an aspirational democratic-Republic will not survive an authoritarian takeover. Since our main authoritarians are self-described Nationalists, the American nation, as they define it, will.
CoViD-19 may get horrific. However, Eurasian civilization and perhaps half or more of its people survived Bubonic Plague and The Black Death, and its harming European feudal society was on balance a good thing. We'll survive CoViD-19, but it's caused by a pretty robust zoonotic virus with the potential for mutations that could ravage large populations.
Climate change from (basically) global warming is a major threat, but civilization and most humans and other organisms — including some large ones — will survive and some may prospser (those of us in hot, dry places, or near oceans, are in serious danger).
As Daniel Ellsberg shows in his much praised, popularly ignored book The Doomsday Machine (2017), Stanley Kubrick did his homework and DR. STRANGELOVE is farcical in tone but documentary in substance. Kubrick's one major error was saying the official policy of the US was that we wouldn't initiate nuclear warfare: our official policy since at least Eisenhower is that, under some conditions, we would (source: Ellsberg and my MilSci courses in the early 1960s). Kubrick got right:
• The public policy of the US is that the US President has "sole authority" over use of nuclear weapons (and can use that authority at any time for any reason: think about that with your least-favorite US President). However, to assure 2nd strike capability, presidents since Eisenhower have delegated authority — or at least have been believed by the relevant people to have done so — to "lower echelon commanders." Whatever their dedication to Central Control, since the Carter and Reagan buildup (and as far as we know continuing since the more recent build-down), the "Ruskies" have done the same. And for the same reasons: credible threat of retaliation in case of "decapitation." In a number of highly unlikely but possible scenarios, any remaining "Launch on Warning" missiles might *be* launched.
• "General Nuclear War" — all-out and thermonuclear — could destroy civilization in the Northern Hemispheres, starting with all those cities that are the root of the word "civilization."
• General Nuclear War with a significant number of ground-burst nuclear and thermonuclear weapons threatens to start a global winter leading to global famines (etc.) and threatening civilization world-wide, and, if sufficiently prolonged, large-scale extinctions of many species of animals and plants and other organisms dependent on sunlight.
The EXISTENTIAL THREAT to humans and a number of other species remains nuclear warfare.
But no b.s. on "destroying the planet" or "destroying life on Earth." "Earth abides," as Ecclesiastes and a post-apocalyptic novel title has it, and life on Earth will survive: the vast majority of living things are non-vertebrates, a number of whom don't need sunlight. Or will survive until the sun goes nova or other cosmic calamity. We might not; a whole lot of vertebrates and fancy-bodied eukaryotes might not. What we arrogantly call "prokaryotic" — like Nature was just chomping at the bit to evolve cells with nuclei — what we think of as primitive life forms will make it through yet again. They were here before us by billions of years, and they well may outweigh us in biomass and/or outnumber us in genes.
But for us, as we think of us, Nukes remain the only Weapons of Mass Destruction and Existential Threat. Let's pay more attention.