Miners don't only make money out of Block rewards (Block reward is the reward in BTC which currently is 6.25) but a miner makes money out of the fee that people pay while making transactions. Because miners are the ones who validate TX and process TX and spend their useful resources (machinery) and spend a huge amount of energy just to earn money.

And with halving, there is no doubt that the block reward reduced to half, which of course a loss for the miners, but as you can see, with each halving, the price of BTC improved and the amount that miners were making in BTC did decreased but in fiat (USD) it increased. I hope there is no need to give an example.

So, I think when the halving in April occurs, the price of BTC will improve and reach to a height where it will be making them the same or more money even from the fee which from another point of view, might be a problem for the TXs makers. But it can be solved using the Lightning network.