Josh Putnam has (as usual) an excellent roundup of the current Iowa/New Hampshire/Nevada imbroglio on scheduling. As I read it, he thinks that it's not particularly likely that New Hampshire will wind up in December; that sounds right to me, but I defer to his expertise on that anyway.
What I'll add is that there are essentially two threats to New Hampshire (and Iowa, for that matter), or for any other state that wants to get or keep a high-profile primary or caucus date. The first, which Josh talks about in his post, is the possibility that the national parties can pursue effective sanctions against them if they don't keep to the authorized calendar. As he says, that's really tough to do.
The other thing, though, is that specific primaries and caucuses take on disproportionate influence if and only if everyone acts as if they have disproportionate influence. There's been some speculation that New Hampshire could lose its importance if it goes to December, but that will only happen if the candidates and the press stay away. Would that happen? Unlikely, I'd say. But I'd say more likely than effective sanctions from the national parties. Basically, New Hampshire and Iowa are important because everyone believes in them, like those flats build by Mystico and Janet -- perfectly safe as long as everyone believes in them.