Let's talk about the facts we know.

Bitcoin miners are currently receiving 12.5 Bitcoins per successful block produced. Which would translate to roughly $87 000 if they were to instantly sell the Bitcoins at the current price ($7000) at the time of this post (April 20, 2020).

Let also take into consideration the costs of mining. One article states that miners roughly spend $4500 in costs per 1 BTC mined. So their total cost of producing a news block would come to $56 250 with the
total earnings of $87 000. The end result is $30 750 profits.

Current reward: 12.5 Bitcoins
Total earnings: $87 000
Total cost: $56 250
Profit: $30 750

Now fast forward to halving. The cost of producing a new block is still the same, but the reward is cut down in half to 6.25 Bitcoins. Let's calculate.

New reward: 6.25 Bitcoins
Total earnings: $43 500
Total cost: $56 250
Profit: $-12 750



It is quite clear that Miners will have absolutely no intention in selling BTC at the current price of $7000 as they will go into a loss.
They have to start selling the BTC at a higher price otherwise it does not make sense for them to mine in the first place.


PS. even if the costs of producing a block are lower than I mentioned, miners would still report a profit loss due to reward halving. To compensate for the reward halving, they have to start selling at higher price.