This is actually a very big red flag, thanks for bringing it to our attention! When people stop mining, they may begin to abandon certain coins altogether and sell off their stash. When it no longer becomes profitable to mine a coin then the only way to make money on it is by trading and speculating on its prices. I wonder if these GPUs would be useful in mining other cryptos instead of ETH/ETC??? Also the difficulty of ETH mining will go back down once they go into the next phase - Metropolis