Why would miners invest so much into electricity for half the reward? I see this ending badly
I think they can't really do the math or hope that some day btc will increase and they'll have a lot more money than they spend on electricity now.
Even after the block halving, the current AntMiner S9's are making more BTC than the electricity they use even in the areas with more expensive electric rates. There is no reason why people who already have bought S9's are going to shut down any time soon.
And if you look at the network hashrate since the halving it has not dropped one bit.
http://bitcoin.sipa.be/