Calling automated balls and strikes doesn’t get rid of umpires; it just takes one task away. There is still going to be an umpire behind the plate. He just won’t have to call balls and strikes. But foul tips, check swings, plays at the plate,etc. still need an umpire to make a call. Heck, tennis has automated in/out calls but they still use line judges.
And baseball has always done what it had to to get calls right. Foul poles, for example, didn’t exist until 1931, because they were better than running ropes up through the stands as extensions of the foul line. (It probably helped that someone realized it was silly to take away a home run because the ball drifted foul after leaving the field of play.). And of course, instant replay is another technological means of ensuring proper officiating.