dave Has the US ever "shown up" to defend itself in a court in another country? Just asking. While I'm in favour of laws-based international relations, surely that requires reciprocity?
Can you cite a relevant case in modern jurisprudence that involves an equivalent magnitude of damages where the US was a defendant? Me neither. Nothing remotely close comes to mind.
In any case, pointing at (hypothetical) bad behavior (not showing up for court) is not an excuse for same said bad behavior on another party's part.
Not showing up for some low-level civil beef is one thing, but something involving the sheer scope and scale of negligence and damages involved here is a whole other ballgame. That gets you a default judgement in virtually every court in the world.
A good analogy is that both Germany and Japan were required to pay reparations for the damages that they were responsible for in WW 2. Of course it took the Allied powers to enforce that.
In any case, if China doesn't want to appear to file an appeal, there doesn't seem to be much to stop the court from seizing their assets in this country to satisfy the debt.