Apart from Biden and Sanders, anyone who doesn't win either IA or NH is done. Everyone else will need the bump in national recognition in order to contend.
Edit: Actually, let me be a little more nuanced.
Sanders is surging because he's consolidating leftist support from Warren. The moderate support is split between Biden, Pete, and Amy. If Sanders comes in first and one of those three moderates comes in second, they may start to consolidate support for later states. Right now the wide field benefits Sanders, and he's attacked Warren at exactly the right time. But if the field narrows and it's Sanders vs. one moderate, he'll have a more difficult time.