There may be a short term small drop over the next few weeks as any high electricity cost systems turn off.

But over the next 12 months I would expect to see a large increase in difficulty.  The hash rate should double or triple over the next year as the S9s and similar 14/16 nm systems come on line.

The S9 currently has a variable cost break even of 30 cents per kWh.  They would still be profitable to run for large miners even if the network hash rate was 4 times higher.  

Over the long term electricity cost and Bitcoin value are the two factors driving the hash rate.  They determine when miners are turned off.  Anyone paying under say 5 cents per kWh can expect their S9 to have a very long life.

So expect a small fall in hash rate now, and a climbing hash rate over the next few months even if the Bitcoin value stays unchanged.