Many people speak of China as if it's one person. Although that may be true in some respects, it's not the case for Bitcoin mining.
There are thousands of miners in China. Each one operates independently not controlled by one person or one organization.
If someone were to say, "What would happen if USA has > 51% of hash?"  People would say, "So what?" There are thousands of independent miners in the USA. 51% in one region or one country doesn't mean anything at all.

As for ghash.io, maintenance fees have gone way over profit returns. People are losing money every single day at ghash.io. Wouldn't you turn off your cloud mining rigs if you were losing money every day? The remaining ones are probably not customer-owned.