well... it will last for some time
you can't predict if the gpu will perform good in some years, because new Game engines will shop up and over years these Game engines will be more demanding and less optimized for older cards
i think with your 1080ti you will play games at 1440p/4k at med-high settings for 3-4 years
5-6 years (1080p med settings)
the 780Ti launched almost 6 years ago and it still plays all the games in med-high settings 1080p