What will happen after the halving is that the supply of bitcoin will be lower (less coins injected into the system) and the price will adjust (each bitcoin will be more expensive because they are more difficult to find).
At the end (long term), the miner's situation will remain the same. He will mine less, but the coins will be more expensive so the end result is the same for them.
Quoting myself on the topic (the relevant parts), lol
Miners will produce only half the amount of bitcoins after the halving, but this doesn't in the least mean that the total supply of coins will diminish accordingly since they don't sell all their coins even now (when reward is high), and they are not the only ones who sell bitcoins. Given that a) they can't increase production (i.e. the number of new blocks found per unit of time, which could potentially offset the drop in reward), and b) they may actually begin suffering losses due to lower reward per block (I don't expect their profit margins to be high due to tight competition), I see it as mostly inevitable that they will have to sell more coins than they sold before the halving (i.e. now sell), in order to cover their expenses (which remain the same per block)
Once the Bitcoin halving occurs, miners will get half as much what they earned before the halving. If their profit margins are not high enough to cover their operating expenses with twice as less (yeah) revenue, they will bear losses and will have to cease mining. But if, nevertheless, their profit margins are high (and they already got back their capital expenditures), then they don't need to sell all their coins in the first place
Unless they (miners) raise the limit and do something with the halving, Bitcoin adoption rate is doomed to stagnate. This doesn't necessarily mean that the price will collapse, but it will if just a few of the top Bitcoin holders decide to part with their stash
In short, things don't work the way you think they should