5 out of the 8 series are currently 3 - 1. If Detroit wins tonight there will be 6 3-1 series.
Based on WhoWins the odds sit somewhere in the neighborhood of 90% chance for the team up 3 to 1 to win the series. A simple model where each game is a coin toss give the odds of 7/8 (87.5%). Those are some pretty good numbers.
However, I am writing this to remind people that there are a lot of 3-1 series this year, meaning that there is a pretty good chance that one team out of the five will come back and win the series. Based on the fact there are 5 3-1 series there is a 40% chance that at least one of the five teams come back and win it in 7 games. And if Calgary loses to make that series 3-1, the odds that there is a 3-1 come back increases to 47% (almost 50-50).
Also, there is 76% chance that one of the 5 3-1 series goes to 7 games.
All the odds are calculated using the binomial distribution.