This line of reasoning is so completely backwoods and grossly misunderstanding of basic currency details.
-China can "collect" any time they want under the arrangement they bought UST under.
-US [bold]WANTS[/bold] China to "collect", "dump" or whatever other improper characterization of the action you prefer.
-US doesn't need foreign entities to loan us money. We want them to so we can export inflation. We have gotten a higher standard of living by doing so.
-foreign reserves denominated in USD can be traded in the international market at any point in time for USD. If China were dumb enough to dump their entire holdings all at once the Federal Reserve would simply buy them all to maintain market stability and we would go on with business as usual, for the most part. I mean, our foreign policy stances and economic decisions would get altered, but for you and I there wouldn't be much noticeable difference day-to-day.