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.