Is Fowler replaceable? Sure, of course. But not easily. Switch hitter, plus defender, high on-base guy, and when he gets on base, the Cubs record was off the charts. Almora could plug in, Heyward could move to center, etc., but the lineup would look different. Lineup construction doesn't matter blah blah blah, but I'm not sure who would be that guy at the top of the order next year