I'm not sure I agree with several of your premises. They're the popular views, but I'm not sure if they're actually true.
The first supposition is that China owns a large portion of our debt - this one I can factually dispute based on numbers from: http://en.wikipedia.org/wiki/United_States_public_debt
Foreign and international own approximately 28% of our debt, and China owns 24% of the international debt. This means China only holds about 7% of our total debt.
Second, and this is just my own supposition, I don't think China cares if they get repaid. As long as their economy flourishes they are happy to allow us to pay cents on the dollar for their items by undervaluing their currency and buying our debt. Think of it as China's "stimulus package" for their economy. Sure in the future they might try to call the debt as a strategic move to affect our economy, but monetarily I don't think it's an issue for them.
If the second item is true then all they need to do is keep us stimulating their economy while ours declines. At the point where they are selling to enough other countries that the loss of our business isn't fatal to their economy they can choose to make any move they wish that harms our economy. If you're playing the long game you only need your enemy to support you until you're strong enough to kill them without doing too much damage to yourself.
I wouldn't be surprised if China is the United States of the next century, in the same way that superpowers like England and Spain were overshadowed by the US.