So the number of defaults is whatever they want them to be, at least in any particular sector. They can control this with the stroke of a few keys and tweaks of policies concerning lending etc..
As long as the real economy reaps real material gains ... and there are no shocks ... then the fiction can continue relatively unabated.
A lot of empty real estate is just fine in a county where more than 300M people still live in the doldrums, meaning, there's some market clearing availability/viability intrinsic to the situation (i.e. 'somebody' will buy the stuff in a panic, even rational speculators, meaning theirs a 'floor' to any panic in that sector, it's not a black hole)
Now if foreign orders for goods falter, that could definitely be a problem.
A real geopolitical calamity ... or something causing disruption to their new infrastructure projects etc. ... could be a problem.
But sans existential crisis there's no reason to panic there's a lot of room for adjustment.
Something to keep an eye on.
EDIT fyi here are countries with whom China has the biggest deficits, i.e. they buy more than import, granted this would exclude major US imports etc. but gives a hint of who is more dependant on China than otherwise:
Taiwan: -US$110.9 billion (country-specific trade deficit in 2017) South Korea: -$74.7 billion Australia: -$53.1 billion Switzerland: -$29.8 billion Brazil: -$29.4 billion Japan: -$28.1 billion Germany: -$25.7 billion Angola: -$18.1 billion Saudi Arabia: -$13.4 billion Malaysia: -$12 billion
So while fewer Chinese buyers of iPhones might not be good, at least the US gets even cheaper stuff of the tons they already buy.
Whereas the Taiwanese will just be bloodied.