Well, China could be less impacted by this (apart from possible climatic changes, but those can occur anywhere), but they still might turn inwise as they did OTL, with a non-developing Europe and Mid-East there are only barbarians outside of China (India depends on how the TL develops), so the Americas might be left on their own for a bit longer.
On the other side, with no profitable European kingdoms to raid, the Vikings or whatever this ATL would bring up might actually focus more on Vinland and this could bring a succesful settlement there, though this still would give Mesoamerica and the south more time. And if they're hit with the, ahem, 'eurasian' plagues earlier (due to more Viking settlers and maybe traders/explorers that travel farther south), they could have recovered from it by the time someone gets itchy and thinks about conquest.