Glenn's death was unquestionably the fault of Negan but was also indirectly caused by the actions of Daryl Dixon. After Negan made his point to the group and took out Abraham, the villain went one further when Daryl chose to pop him in the face.
After a bit of a rant, Negan beat Glenn to death to make his point when seeing that Daryl clearly did not understand.
Many fans immediately blamed Daryl for Glenn's death. We haven't had a chance to see how the other characters feel yet, given the follow up episode took us to the Kingdom, but according to Norman Reedus no one blames Daryl for Glenn's death except himself.
Here's what Reedus has to say about it:
He goes into a very dark place. He completely takes the weight of that and just carries that with him. He never forgives himself and he takes full responsibility. Although the thing is, Daryl didn’t say “Oh if I do this, they’ll kill Glenn.” Nobody knows what’s going to happen with that guy with the bat. Nobody knows anything. But what he was doing was protecting Rosita. Negan had that bloody bat, waving it in her face, yelling at her, and it’s right in front of my face too. We were right next to each other. And he was picking on Rosita and Daryl stood up for her and he stood up for Abraham. The outcome of that, nobody knew that was going to happen.
[Jeffrey Dean Morgan] and I were joking in the car coming to Talking Dead, and I was like “Man, I hope people don’t think it’s my fault. I’ll catch a lot of flack for that.” No one had ever said that to me before. No one was like, “You’re gonna get it! We blame you.” I was thinking of it, and the characters don’t blame me or anything like that, but Jeffrey was teasing because he was saying people were going to hate him so he was joking that he was going to be like, “I’m just gonna tell them it’s your fault.” And I was like, “Don’t even think about it! It’s a mistake. You do it on Talking Dead in front of 10 million people, everybody starts to think it now!”
So he was kind of apologizing for it. But the truth is that whole group on that show would have done anything to protect any of us, and that guy’s crazy with the bat. The weight of Glenn’s death is going to weigh on Daryl heavily, I know it does. He gives up, he loses the fight, he’s keeping to himself, whatever’s happening to him, he thinks he deserves it. He’s going to let it happen, which is crushing. To take somebody wild like that — a wild, pure, honest fighter like that — and just strip him of his desire to fight back or fight for anything, it’s crushing.
The aftermath of Glenn's death will be seen, at least from Daryl's perspective in this Sunday's new episode of The Walking Dead. However, we will have to wait one more week until we see the lasting impact in effect on Rick, Maggie, and the rest of Alexandria.
As for what's in store for Daryl Dixon, Reedus tells ComicBook.com he is a "prisoner of war." Negan will attempt to break him down like an animal and see him transform into a loyal servant of the Saviors. Will it happen?