Not often I'd think, because when a team wins a world championship there's undue pressure to keep the team intact far beyond their expiration date. Recently though, you could point to the 2004 Red Sox (Pedro, Lowe).
The Blue Jays lost pitchers that started nearly half their games in 1992 (Cone, Key, Wells, Stieb), plus their closer (Henke), and won another title in 1993. Getting Dave Stewart helped offset that somewhat, though.