That is not how the mining works. The difficulty changes depending on the current total hash rate of all the miners. The more miners the higher the hash rate so the higher the difficulty. The system automatically adjust so the 12.5 Bitcoins are made/issued roughly 10 minutes. So it really does not matter how many miners are on the system, 12.5 Bitcoins are always issued roughly every 10 minutes.
As a miner though, the more miners the harder it for your miner to be rewarded the 12.5 Bitcoins. That is why pools were formed to group up the pools total hash rate to improve the odds of being rewarded the 12.5 Bitcoins. As a member of a pool you are receive a portion of the 12.5 Bitcoins based on your miners total hash rate minus the fee the pool charges.
If the Chinese actual ban mining, the benefit for the rest of the worlds miners is a lower total hash rate which again lowers the mining difficulty and increases the odds of be rewarded the 12.5 Bitcoins.