Cheers!
Well, that possibility always exists. The only question is, what is the likelihood of it happening. And China's current economic dynamic points to continued growth and not an implosion.
Most of China's debt is internal and not external. That's why the Japanese government, with a debt of 200% of GDP hasn't had to face the same difficulties as Ireland, Greece and Portugal, even though those three countries have lower government debts as a % of GDP than Japan. A slow bleed, maybe, but not an imminent default.
And while we don't know the degree of China's internal debt, who is to say they are crushing debts, it could go the other way in that it turns out not to be so debilitating and is manageable.
In recent history (past few decades), there are three well known cases of economic calimity, Argentina, Brazil and Russia. In the first two, both Argentina and Brazil had external debts that were debilitating. And Russia, made a sudden transition from government ownership of industries to private ownership overnight.
China has neither debilitating external debts nor will they make a sudden transition. That's why she is resisting calls for a sudden appreciation of the yuan and only allow about 3%-5%/yr.
Things could always go wrong, unforseen circumstances, etc., but unlikely. However, I do feel it is likely that China's GDP, by 2020, will be slightly larger than the US.
2011 was the year it was made official that China surpassed Japan as the world's second largest economy in 2010. It was news, but it really wasn't news. The year 2021 will be the same. When all the numbers come out, it will be made official that 2020 was the year China became the largest economy in the world. And by 2021, much like 2011, it will be news but not really news at all.