Even though the current proof of work algorithm is really dirty, and make a lot of energy waste especially in the electricity and don't forget the whole Bitcoin miners make a lot of CO2 emissions. I'm sure cryptocurrencies mining will everlasting because the GPU creators will have a lot of profit from the cryptocurrencies mining.
GPU creators profiting means that cryptocurrency mining will be everlasting? - Doesn't add up to me
POW will either be replaced or it will become far less of an issue as renewable energy sources are explored. Everything is either improved upon or replaced, it cannot remain static.