Already happened. The hash rate is falling and the market is flooded with cheap hardware.
You'll hear some handwaving about difficulty adjustments. That doesn't change the fact that it is becoming increasingly unprofitable and miners are already shutting down en masse.
There are tons of interesting failure modes. The simplistic one won't happen, but that doesn't mean that it isn't teetering on the bring of a death spiral.
What happens when the market is flooded with cheap miners? A 51% attack is suddenly affordable.
What happens if the price drops off a cliff right after a difficulty adjustment? As hash rate falls, difficulty adjustments become farther apart than the two weeks they're supposed to be.
What happens when smaller miners close up shop? Bitcoin mining is already very centralized. Falling profitability would move it even more into the hands of the biggest players with the most efficient hardware and the cheapest electricity. Read: China.
A falling price is a huge problem for the security and stability of the network. Bitcoin is teetering on the brink of complete collapse.
>people still want to transact Bitcoin
No one uses Bitcoin. The transaction fees would have to go up by a factor of over 100 to equal the current block rewards. And, if people don't use Bitcoin now, why would they when transactions are 100x the current price?
"Your money is safe because it's not worth anything anyway."