First of all, I have no firsthand knowledge of official policies or how Northwestern operates.
But...it is worth noting that several years ago, all Big Ten schools agreed to award four-year scholarships to their athletes, which I think was a very public and strategic move to contrast our programs from those in the SEC (and elsewhere, but especially the SEC) where kids would have to worry about whether they'd be renewed from one season to the next.
Entering the Portal does not officially or specifically resign a player to leaving the program...they haven't officially left until or unless they do. This system heavily favors the player and compromises the program's ability to prepare.
I would be in favor of a policy where if the student enters the Portal, the program has the right to make personnel moves with that scholarship (including, if they choose, to hold it for the player exploring his options).
On one hand I think to myself, "that would be like a company replacing an employee for them acknowledging they were looking at other jobs," but as it stands, we have a ruling that players aren't employees...