The league has the power to correct their mistake. Like taking out the standing in the crease rule after recently putting it in, they can change the rules back, even if not all the way, some of them. Remove the instigator rule and if two players fight there is no extra penalty for two willing combatants. It allows for the players to help police the game and start fights at all times of a game. They could take it further and eliminate the instigator in the last 5 minutes rule, which leads to suspension. Taking away a potential loss in pay will make it more financially advantageous to fight. They could eliminate the mandatory visor rule. Players were going in the direction of visors without the leagues help. Not making it mandatory allows for tougher players to leave it off and take part in more fights. This would protect the fighters hands and make it easier to connect with the face through punching. They should reduce suspension length. I also think using the option of fining players more and not suspending them from games would allow players more freedom to try to make body contact through hitting. More hitting then there is more fighting, more fighting and there is more hitting. It leads to more passionate games and rivalries. It also gives a losing team a reason to watch blowout games and their team in a losing season. The league should promote physicality more. Giving the players a reprieve on the rules should see a return of passion. With the high scoring games similar to that of the 80's, a faster game with a high level of physicality may be the best hockey to ever be played.
I don't think they'll ever come back on plays targeting the head because of concussions. But, reducing suspension length and not over penalizing plays not targeting the head may see a resurgence in body contact. If it pays for the player to play more physical they are likely to. I also find it unlikely they go back to the days of Peter Worrell and Matt Johnson style heavyweights. Players being able to play hockey should be necessary for NHL level play, if you can't keep up and are a serious detriment, I think they've moved past it. That has no bearing on fighting not making a comeback though. I think you can sacrifice the size and effectiveness of the fighters on teams to make sure that they can first play the game at an NHL level.
I think a serious fan pitch. Some type of petition that gets media attention that gets to all fans begging the league to make the league more physical may get the ball rolling on this idea. There are more positives than negatives for the league if they were able to make it more physical. Violence sells in hockey and they would receive more fan fare. If they can maintain a high scoring game they may be able to challenge other major sports in popularity in the US and it would certainly become more popular in Canada as well. More eyes is a win for them. Them providing the most entertaining product and not the most safe product is most important.