A difficulty adjustment like that would also depend on when during the current period the sudden drop of hashrate occurred. If it happened at the beginning and lasted for most part of the current difficulty period of 2016 blocks, the difficulty would be reduced more than if it happened in the middle and especially at the end.   

When you say temporary, do you expect the hashrate (the miners in China) to resume their operations soon or do you think the machines will move abroad and mine from somewhere else? I don't think neither of these two options will happen that fast.