He 100% will be granted permission provided that there are no further incidents, there is zero doubt about that.
It is possible that he is granted permission at the start of the season but likely only if he is going to make the team. I do not expect him to be officially allowed to play in the NHL until he is officially being brought up and that is more likely to take place in season or nest fall. He is not an NHL player as of yet and there is zero impetus for the league to be charitable in a PR situation such as this and unnecessarily put themselves up for criticism.
If he never plays then they never have to make a statement that is guaranteed to draw criticism from the radical activists who are chomping at the bit to attack Bettman and the league. There is nothing to be gained at all by the league by doing this until they absolutely have to.
As
@WeThreeKings pointed out earlier, that Bettman (I disagree on this one minor point as it is a league ownership issue and he is their spokesman) already royally screwed up the Pride night fiasco by backing down and enabling ignorant mindsets to continue to marginalize minority groups. This is a sign that perhaps Bettman and the owners will bungle this as well and put themselves at risk for criticism by unnecessarily and prematurely granting entry to the NHL to Mailloux.
Anyways....this topic is almost certainly a nothing burger as Mailloux will be granted permission to play and he will be able to play the very instant that the Montreal Canadiens deem him to be ready.