if china dumps the holdings it will be at a loss. there is money lost. China is the seller.
end of discussion
Actually, it depends on the market value. I don't think you understood what the poster said when the poster say US Dollar will devalue and Yuan will basically shafted.
People won't buy T-Bond if they know the price is going to pummel and the only way people will buy is the interest rate is spiked, but US won't stand there and look at a spiked interest rate, they will do something to limit it
Which mean US will install monetary policy to cap the interest rate spike, which mean they either inject more money in the Treasury to hold the interest rate and keep the flow, or they print more money to hold the interest way to keep the flow. Seeing why there are T-Bond in the first place, Reserve bank won't be able to inject more money into Treasury apart from a major tax hike, which mean US will print more money as in QE package to curb the interest rate.
On the other hand, Chinese Yuan will be destabilised as most of the guarantee of Yuan is in T-Bond, release them all will basically drain out most if not all of tradable foreign currency value in China, Yuan will collapse. As long as China is developing, needing more money to develop, they needed to absorb large amount of T-Bond, which is the only thing stable enough to guarantee a future return. So using T-Bond as a weapon is a non-start to begin with.