If the flooding actually ended up doing damage, halting the operations of the miners, then undoubtedly there will be a decrease in hashrate. How big/small will the decrease be? That's probably the better question. I don't think this will have any effect on the price at all. It's not like Bitcoin will be super unsecure once some of the Chinese miners turn off their machines.
Tragedies like this can really cause a huge impact to an economy.
But for China, I don't think that this is a huge problem for them. They have a stable and well-grown economy so to rebuild those destroyed establishments for them is really not an issue. These flooding can really tear down all of those existing businesses in their country. We all know that in China, there are a lot of bitcoin miners, maybe this can affect them the way they think about their safety.
Just like what happened in Beirut, Lebanon, this tragedy can really affect all parts of the economic sector, including cryptocurrency or any assets that they store in their houses.