The most important thing is that even if the hashrate declines, it will not compromise the security of the Bitcoin network. As to the Bitcoin price, it surged close to 20 percent. This is an indication that the halving event is regarded as a good thing for the Bitcoin industry and it is positively impacting the market even before it takes place.
The hash rate will only drop about 10 to 20%. Then the hash rate will increase again due to more efficient miners.