I think that's quite absurd. If Sanders wins Iowa and leads in New Hampshire, then he becomes the front-runner, let alone a serious threat. I would say he's already a serious threat to her.
Disagree strongly. Hillary is still regarded as the strongest frontrunner in modern history. Very much will have to change for her frontrunner status to evaporate completely. Also Sanders is regarded by almost everyone who is not a Sanders groupie themself as close to 100% unelectable. That fact won't change (much, if any) even if he were to win both Iowa and New Hampshire.
Sanders is almost as unelectable as Trump or Ted Cruz in fact.