When ETH goes entirely to POS, it will be the end of ETH, or at least they will face many problems. POS consensus mechanism is not as reliable as POW. But I would like that to happen so that we can finally see how POS works in a practical environment which is competitive enough to pose challenges to the algo. The weaknesses of POS will be come visible very soon after the shift. As for the miners, the miners will switch to another coin, or several coins which they think are the most profitable. ETC may be among those coins.