There is a lot to talk about here.
First off, none of us really knows what goes on with a team behind the scenes: on the plane, in the hotel, at team meals, etc. With social media we like to think we do, but we don't. Coaches love Glass and it has to be for the invisible stuff we don't see. I asked my son-in-law, who is a Pens fan, about Glass and he brought up the off ice stuff too. There is something about Glass that makes him repeatedly get jobs even though he is a pretty poor hockey player. Worth the money? Not to me, not to you, but to Sather and AV, apparently yes. I much rather have kept Dorsett, but there must be a reason why we let him go so easily even though he is more skilled than Glass. Off ice, stuff? We'll never know. Off ice, as well as one ice issues, is likely why we got rid of MDZ. JT Miller may have been banished because of off ice stuff too. We can speculate about what goes on behind the scenes, but, seriously, we have no clue. But even with that said, Glass needs to start contributing on the ice or he will be gone.
Next, it seems to me that the role of the 4th line is changing. Though I like the "old idea" of a 4th line: energetic, physical, strong in possesion if not in skill, we seem to be trending to more skilled 4th line players. Guys with a limited skill set, like Glass, Carcillo. or enforcers, are on their way out. Its like in baseball, where middle relief guys are now skilled hard throwers instead of just the least skilled pitchers on the team. Coaches are demanding more from their 4th line. By the way, in the last years of the Original Six, when I first became a fan, there were no 4th lines. Teams dressed only 11 forwards. The extra two were often PK specialists and filled in as needed.
Face it everyone, a victim of the stress on skills will be the end of fighting. In ten to twenty years it will be gone. Enforcers are an endangered species because of limited skills. Couple this with the concussion and head injury issues which are a big deal and getting bigger every year in all sports, the NHL will eventually ban it. They will have no choice. I too grew up with bench clearing brawls, but I've come to hate fighting. As it exists today, it is stupid and pointless. I love physical hockey though.
Not only enforcers will be gone, but limited skill guys like Glass too. We are in the last years where a guy with little else but intangibles only can get contracts. Future 4th line players will be asked to do more and have more skills. The game is evolving. Jesper Fast on the 4th line? That is a glimpse of the future.
Last, someone cited Avery and Tikanen. These guys were not 4th liners, but skilled 3rd liners.