People leave bitcoin mining for good? No, it cannot happen long term. It is a self-regulating feedback loop. You see, when the profitability drops, people leave mining, hashrate drops, then as a consequence difficulty drops and profitability rises.
This sounds wonderful in theory. In reality, I believe that some miners do mine at a loss (some know it, some not) and some of them even leave this business for good.
But the chance is bigger the miner keeps mining at a loss than coming back after leaving this.
What you may have been seeing are short term fluctuations. Even the halving didn't hurt profitability long term.
Care to elaborate a little? Halving doesn't necessarily get reflected in the price and I am sure that halving the income for the same work (the difficulty won't drop) and consumption is not great for profitability.