At this point i think it depends heavily on how well the other teams in the West are playing after christmas. If they get pounded by the Ducks, Oilers, Flames, Ducks, Hawks, Wild etc. playing their best hockey every other night and at the same time Vegas regress, they could fall, but that being said, they're in a fine position right now and aren't winning games in flukey fashion.
Playoff race in the West could be fierce this season.. So many capable teams are either outside looking in or in just by a few points and almost no one is able to gain notable ground (and Preds and Blues both lost to Vegas so they will be looking for revenge). It makes for tough nights every game, which is going to make bouncing back from a few losses very tough. I think the East will be different in a sense that the teams competing will be pretty clear at some point, where as in the West only 2-3 teams will probably be out of it early (personally think Arizona, Vancouver and Colorado can't keep up).
Then there's the spoiler teams. Getting it done against the weaker teams in the East will be crucial, but that's where your quality of roster comes into play and on paper Vegas isn't really that much better than teams like Florida, Detroit, Buffalo etc. So if you're not playing well and losing confidence, it's possible to lose these games especially when you're supposed to win. Heck, it happens to better teams than Vegas every year.
So the makings of a freefall are there, but Vegas holds their own destiny which is great for them. Odds right now are in their favor.
I voted for them to win the cup just so i can say i knew it.