They will not suffer losses once the mining farm is operational. As long as the farm is mining, I can safely say that mined coins will always cover operating costs. Contribution to invested capital will be slower after the halving, but it is still profitable to continue mining.
I'm singularly curious if you argue just for the sake of argument. 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...
You are granted an opportunity to choose where exactly you fail