China pulling out of the bond market though would signal risk to other investors, which surely would increase bond yields. As yields rise, wouldn't the availability of investors decrease as it did with Greece. I don't think it'd cause significant harm to China, they'd still have other markets they can export to, especially the rise of India, Kenya (which is doing fairly well and has a good relationship with China) and Latin America.
In terms of the gold standard, many financial market websites are seeing a shift in Chinese monetary policy. But who knows, it's all hypothetical, but I thoroughly enjoy these debates.
So do I!
I'd say in a situation where the US and China declared war, the U.S. would cancel all debts owed to China. Despite China holding the lion's share of Treasury Securities, those securities only provide benefit should the United States honor them. That'd harm both China (missing out on 8% of 16 trillion US Dollars!) and the US, i.e investor decrease. If China chose not to declare war but instead sold of treasury securities it would impact the United States' ability to import goods from China, which would hurt China. So I still say it's bilateral, yes the US would in a very bad position overall, but it would significantly dent China's finances as well. They do need to keep the balance or both risk losing out,