I don't know why people hang on world of yesterday so much, or even their memories. Maybe that is what makes us human. Memories and the ability to recall them - even though it's evident that those memories are present in the animal kingdom as well. I feel sorry for Maggie being in the hard place, again. It must not be easy for her. Then again, it's clearly not easy for anyone, Deanna on top of everyone.
She lost her husband, then her world, before she almost lost her life for not understanding to go for the head. The grief can put you in a strange place. It can literally numb you for good. You can walk around a glass stuck on bottom of your feet, and you won't feel it. But, in reality, in the present, there's no time like now. You must harden yourself, and build a wall around your hearth.
It would have been easier if Reg had wandered away because at least then Deanna would've had hope. Same hope that Maggie is hanging to, and it's right for her to scrub Glenn's name off from the wall. Same thing goes for all the other names in that list just like Aaron said. He might have made a mistake that lead to death for many Alexandrians, and off all people, he should have understood the danger. After all, he made it clear in the last season that he observed Rick's group for a while before he delivered them water, or even showed those damn photos.
Nevertheless, Wolves could have done the same. They could have stayed in the distance and just followed the group to Alexandria. And even if Aaron had retrieved those damn photos, same thing could have happened. In fact, you heard that in Rick's explanation, when he said, "Carol told he got one more, but she couldn't find his body. So, he must have been hiding under there..."
It's so easy to make a mistake that cost lives. I was afraid Deanna was going to pull the gate open at final shot and let the dead do the deed. There's no life inside the wall. In fact, Alexandria at the present situation could have been inside the Prison, and those damn zombie a hoard to wanting to trample Hershel's garden at the front yard.
A question, what would you do to clear those zombies?