If the Blues either re-sign Miller OR reach the Western Conference finals, Buffalo instead of getting that third-round pick, gets the Blues' first-round pick this June (they have the first-rounder in 2015 from this deal); but St. Louis would then get Minnesota's second-round pick this June (obtained earlier by the Sabres) plus Buffalo's third-round pick this June.
http://espn.go.com/blog/nhl/post/_/i...er-pick-change
This makes the trade a little more even giving up your first three years in a row would be tough without having a lot of seconds to back it up.