If he loses MA, MN, CO I think it is effectively over.
He would be better in the states in the next two weeks, but he won't be able to get enough momentum and narrative to win.
If he wins MA, MN, CO, and Vermont, he shows that he can win. In fact, if we wins all 4 I would put him as the favorite to take the whole thing.
I'll make my prediction. Bernie wins MA, but it is close. I think he wins Colorado. Minnesota? It would honestly be a blind guess. It will be close. Theoretically caucuses should favor Bernie (enthusiasm intensity), but he has lows both caucus states so far.
It is crazy how poorly he does with African Americans. Based on their records I think it should be a bit more of an even split. Interesting polls show that while white democrats have moved left, African americans haven't. The fact the he is not religious and a white jewish man could play a role in limiting his appeal to more conservative democrats.