I'll never forget the '93 playoffs, where both the Blackhawks and Bruins were #1 seeds - 21, and 23 points ahead of their round 1 opponents (Blues and Sabres), and both were swept 4-0. Boston had gone into the playoffs 8-0-0, and won 18 of the final 21 games.
Their season ended with the infamous May-Day goal; Chicago ran into CuJo, and go shutout twice in the sweep.
I also remember the 2001 playoffs, and the running joke around town was that the Leafs were so out-matched that they were gonna lose to Ottawa in 3. Turns out, they swept the Senators.
Anything can happen.