If the .us TLD vanished, as in, if America ceased to be. I imagine com, net, org, and domains of the like would also be seriously affected since their maintainers as well as the organization with all control over all domains and the root servers would also be affected by such change. The internet could adapt for sure even in the worst case scenario, but with how centralized DNS is it would cause more than a few shakeups. Probably would make this incident look like a drop in the bucket.

Exactly this. Another factor in choosing TLDs is that they have different rules. Read those rules closely. Some of them make it much easier for them to take the domain names away from you, for things like copyright infringement, for example. .COM/.NET/.ORG have the strongest rules protecting your ownership, as far as I can recall. This is one of the reasons I stick to those old 3 rather than using newer gTLDs like .INFO, .BIZ, etc.

Yeah, my domains are .com or .us, the .com ones face the outside world for whatever reason and the .us I use to mean "us my family" rather than US, though I'm a citizen so I'm in the clear

If .us suddenly goes somewhere its prrrrrobably true that I am also gone in whatever caused that, too