To answer the OP... how about Stan Smyl not cashing in on a breakaway in Game 7 overtime vs. Calgary in '89?
Calgary came back moments later with Joel Otto "kicked in" the winning goal. The Flames went on to win their only Stanley Cup.
Depressing result (I had been cheering for Van in that series), but man, if you go back and watch that entire overtime now, it's amazing.... End-to-end chances, both teams just going for it, all out. No "sit back and wait for a power-play because the coach will bench me if I express my natural talent" like in today's game.
That Smyl save was exciting, but as someone mentioned he basically fired it right into Vernon's glove. I like the save Vernon made on Tony Tanti just before (?) that, because Tanti wound up and really fired a laser that was labelled, but Vernon got it somehow.
(Tanti, a 40-goal scorer, wasn't what you call a playoff stud for the Canucks -- 18 playoff games, 1 goal.)
EDITED TO ADD: I found the clip of Tanti in overtime:
And btw, if you watch the highlights of that overtime, about 5 minutes before Stan Smyl's partial breakaway he makes a great move from the side of the net, fools Vernon completely... and hits the post.