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I don't know how this can be sustainable. With each block reward halving, less and less coins will be mined. If the prices don't go up exponentially, then sooner or later these mining farms will be forced to cease their operations and file for bankruptcy.
I think the more probable scenario is that only a part of miners will quit the game. And for those remaining it will be easier to get the rewards, so they'll stay. Even at today's prices, around $4,000 per 1 BTC, mining rewards are pretty inspiring.
12.5 x $4,000 = $50,000
That's how much, plus transaction fees, miners are getting currently every 10 minutes. Just think of it, those are decent monthly earnings for 25 people. Since approximately 4,320 blocks mined per month
4,320 x 25 = 108,000
we can see that at least 100,000 miners would remain today in a any case, and at least 50,000 miners would remain if the block reward were two times smaller than it is currently.
I'm not saying the price of BTC will not rise, but that will happen rather because of the higher adoption than because of the upcoming halving. Miners don't, and can't, dictate the prices.