Again, you don't need to guess. These are calculated for us with algorithms and facts.
I didn’t read the methodology, but the probabilities likely account for current standings, remaining schedule (including #of games left, quality of opponents, home/road games) and quality of team, based on current record (which also accounts for GF/GA). So the Habs’ quality of team is based on current standings, which includes Weber being injured for half the games. Assuming that the team is much better with Weber playing all games, then the Habs should actually have a better chance than 74% or whatever the current chance, provided key players stay relatively healthy. What I don’t think the simulations account for is the probability that something disastrous like Price getting injured happens that tanks the season (like in 2015-16).