There are a few coins out there that 'pride' themselves on being asic resistant. Vertcoin for example. So I don't think GPU mining will die when there are popular coins out there who intend to keep GPU's as the main form of mining.
Sure profitability might drop, by don't think it will outright 'die' in 2018. Also ethereum going POS won't help with hashrate distribution.
profitability won't drop as long as you keep updating your cards to the latest generation ones. Mining is here to stay. People like to say mining is too easy profit to be sustainable but they don't know the trouble that is to setup consistent rigs and monitor them over time.