I'm basing it on articles that I have read with comments from both the players and the teams involved. Some are linked on the front page of USCHO.
I agree that there is a strong chance that all 3 will not be in the NCAA ranks this season.
From what I have read/heard, Kessel is the least likely to be back. It seems to me that if he gets an offer from Boston that he will bolt. EJ and JT are both tougher to read, as both of them are so young. The comments from those two seem to indicate that they will do what their teams want, but Toews' comments seem to imply that he feels that he needs more work before moving on.
We'll see I guess. Maybe I am way off-base here, and PK and EJ will stay at UMN, and Toews will leave.