I don't have any great concern if Johnson or Portillo opt to go elsewhere. It would be disappointing, no question, but the player has rights as does the team. NHL teams draft lots of players who then become their property for years only to decide not to sign them (see the Sabres recent decision to not sign any of the three late rd D-men from the 2018 draft, whose rights the Sabres held for 4 years). What's good for the gander is good for the goose, as they say.
In Johnson's case, lots has been made of the potential influence of his father, who is a development coach with the kings. I suspect that his father's main influence is not in directing him towards signing with a team other than the Sabres, but rather comes from a belief that his son's development is best served, at this time, by the college path as opposed to the minors. The additional benefit is that at the end of this year if the Sabres don't have an NHL spot for him, he can go to all 31 teams and gauge if there is an opportunity to step right into the NHL in 2023. Hard to blame a kid for choosing that path if that is what he wants.
Ditto for Portillo; if he thinks he will develop well with another year in college and if he, perhaps, sees Levi as the goalie that the team is most invested in, then it is entirely fair that he exercise his right to explore other options. 3rd rd picks don't turn out for a lot of reasons; one of those reasons can be that the player decides the team isn't the best fit for him. If the Sabres can opt not to sign a drafted kid to a contract then I really don't have an issue with a kid deciding to pursue a path that is better for him. This is made easier to swallow when it seems the reasons may be more about opportunity than by any bias against the city or the organization.
At least with Johnson we will get the compensatory late 2nd rd pick if he goes elsewhere. If that's what happens and we end up with four 2nd rd picks next year, I won't be overly down about it.