That's wishful thinking.
Unfortunately, it doesn't work that way. Their goal is to extract the maximum value possible. Think strip mining. They will pull every last cent that can be economically retrieved, and they'll do it as efficiently as possible. The final result will be the same regardless -- no remaining value.
If you think the currency won't devalue because China is afraid to start extracting, well, that's like suggesting that a mining company is afraid to start stripping because they might jeopardize the stability of the load. Careful maybe, but afraid, no.
To be more specific, China has no choice in the matter. They purchased this mountain of money, and if they want anything at all back, they will have to mine it. Doing so will reduce its value, and unfortunately, the lower-bound on the price of the dollar is actually its value as used fabric/paper.
Here's the mechanism.
China: US government, you owe us $100.
US: We don't have it, but we'll print up $100 for you right now. Here you go.
China: We figured us much and thanks for the $100. Global market, we'd like to buy $100 worth of copper.
Global market: Done. Here's your copper. Oh, and since you bought it and are not putting it back in the market, the price of copper just went up by $1. Come back soon.
China: US government, you owe us $100...
Global market: I just traded copper for $100 that I know were newly minted. I better trade this quickly for something that will hold value or I'll get stuck with it...
And so the new dollars disperse into the market, China converts dollars to metals, and prices in dollars slowly rise as everyone who touches them quickly trades them away. Eventually someone gets stuck with them, either because they were too slow, or because they were on the losing end of a currency exchange option.
This is happening today. The input is continuous, not a unit step function at $100 a pop. The output may seem slow and linear now, but the rate is accumulative, so it's reasonable to expect exponential factors to dominate.