Not possible at all. Miner's electric cost alone is around $150-230, depending on geography location. So if the price dropped below that for long term, many miners will not be able to survive. And this will pose serious issue for Ethereum ecosystem.
I strongly believe $250 is the floor price for ETH currently. Until Casper (/Hybrid) launch, where the dynamics will go through major change and adjustment.
The mining costs have nothing to do with the price of a coin, if the price of a coin goes below mining costs then that means that the miners will have to choose, keep mining for a loss for some time? Or to stop mining ethereum and mine something else? That's all, the only ones that have to care about the cost of mining are the miners, but the speculators, investors, traders and long term holders do not care about it.