Denver knew they were outgunned when it came to offensive talent and they played the conservative defensive trap game perfectly. Combine that with an outstanding goalie performance, and you have a recipe for an upset. After they got the first goal, it was clear that the rest of the game was going to look like an early 2000's Devils game.
BC needed to change strategies when it was obvious they were having trouble breaking the trap. The DU goalie played well, but he wasn't facing many high difficulty chances until the third period. They needed to get more traffic to the net and look for screens and greasy goals. There wasn't enough desperation in their game until later on, but it was already too late.
Not sure if Leonard will go pro or not. I think his odds of coming to the Caps next year would be greater if BC had won. Being so close to winning a championship could inspire him and his buddies to stay another year, but there are just as many reasons for some of them to turn pro. Their team will probably look a lot different next year.
Personally, I don't think Leonard has much more to learn at the college level. I wouldn't blame him for staying another year for his own personal reasons, but his career development would be best served by coming to the Caps. Guess we'll just have to wait a little longer to find out.