Foxconn is already replacing workers with robots ("Foxconn replaces '60,000 factory workers with robots'" https://news.ycombinator.com/item?id=11770463) and I'd argue so do car manufacturers for 50 years step by step. I don't know if they could reach 100%. In other industries, e.g. food processing, it seems humans are only needed to fill up the ingredients, watch monitors and do QA.