It's a little more complicated than that. Assuming you are correct about the 6 Chinese miners controlling > 50% of the hash power they could indeed collude and

It's a little more complicated than that. Assuming you are correct about the 6 Chinese miners controlling > 50% of the hash power they could indeed collude and support a new block size. When the first large block arrives the blockchain splits effectively creating a new currency. Old Bitcoin and New Bitcoin. It's the Bitcoin infrastructure in terms of exchanges and wallets that will decide which of these coins will be the winner. Basically if you have 1 Bitcoin before, then after the split you will have 1 Bitcoin in each chain. The market will decide which of these coins will hold value. It's not the first time the blockchain has split.