It's highly unlikely that 20% will disappear overnight. Every other case where we've seen automation/innovation eliminating jobs has been a gradual process, so I see no reason for this not to continue.
Amazon has been testing cashierless grocery stores, yet they haven't completely eliminated their competition where they're available. I'm sure they'll become popular, but they'll likely roll out relatively slowly. We already have self checkout, yet some people prefer to checkout with a human, and I doubt that will change.
Manufacturing jobs have been using more and more automation, yet manufacturing jobs are still available, just different. Many jobs that used to be minimum wage jobs have been replaced by higher paying jobs with specialists; there are fewer of them, sure, but they pay better.
As labor jobs get replaced by automation, we'll invent new jobs to take advantage of the increased labor pool. That's just the way innovation goes.