Below is a great article that talks about the future of Ethereum mining--they state that it can probably go on for another 6 months, but once Metropolis, the proof of stake platform, comes in, who knows??
I always find it weird when miners don't change with a coin. Like Ethereum Classic. That was a bunch of guys unwilling to change with the coin, and Poloniex making sweeping decisions. It doesn't matter in the long run, I mean who really cares, but with the Bitcoin fork(s) coming, we could be looking at 2 or three different types of bitcoin coming down the line.
Will miners refuse to stop mining the old/new Ethereum? We will have to see. The next 6 months in crypto, whatever you invest in, are promising to be a wild ride!
https://www.crypto-news.net/what-does-ethereums-proof-of-stake-algorithm-mean-for-miners/