I am however in agreement to your statement that when ETH goes POS, GPU mining will surely come to an end because of the difficulty rise on all other coins. It might actually be better to sell GPUs today while they still can still mine. When profitability goes to 0 the market will flood GPUs even more so.
Yeah, more miner giving up, more chance to miners whose stay. We can sell all of our graphics cards before GPUs price going down, but we can't predict for sure what will gonna happen next. If GPUs mining back to the top, we can get it back easily.