Most of the bitcoins gained by miners are being converted into fiat to support the operation of the mines. Miners will want to maintain their income/cost. Therefore reward halving will results in miner seller coins at higher price in order to cover the cost and get income.
Without an increase in price after reward halving, the mining operation will become unprofitable.
It is not the miners who decide the fiat their mined BTC will fetch... it is the market. When reward halving strikes BTC, there will be less BTC offered to the market - by definition of course - this suggests all other things being equal that price will appreciate. Also, there are many other factors that will come into play at that time - I am not so sure price will double instantly!
If price does not increase, well the less profitable miners will cease their activity until enough have quit to make it profitable again.
Let's also not forget that the aim of the BTC adoption campaign is also to have more transactions going on by that time; with increasing transaction fees paid to miners this might reduce the negative impact of reward halving!
Mining long ago stop to be profitable, bitcoin was created under different terms now big investors mine the coins and push the price down till made unprofitable another mining operations. Plus bitmain before sell the hardware they mine a month for themselves
Miners already stopped operations before December of last year, bitcoin price is controlled by the Chinese market.
with the halving the price raise up before a big fall.
they need to buy couple more of millions of coins.