I always find it interesting when a team has a star player who seems to be a key piece, probably their best hitter, making them competitive but then he leaves and only after that do they win. Watching the Nats dismantle the Cards the last few days and wondering what Bryce Harper is feeling right now. I know there are many examples of this, who can name some?
Foremost in my mind is Billy Butler leaving the Royals after they reached but lost the WS, and the year before they won it all. Butler obviously wasn't the Royals' big star but he'd been their homegrown guy and, from my point of view in the hobby, my favorite Royal. Frank Thomas played a handful of games the year the White Sox won, though he hadn't been the 90s Frank Thomas for some years.