DClock takes place months in the futre and hasn't occurred yet in the other books. I suspect everything will be caught up by the last issue.
"Former glory" is up to interpretation. Some of us might like it; others may not. But I'm pretty sure the story's ending with a combination of familiar and tweaked. It's been decades since any comic book having a longer time change story has reverted totally back to the way things were. There's always been some sort of change.
I'm speculating (a fancier word than guessing) that most of the changes planned are happening in individual books like with the Superman stuff. Hopefully the ending of DClock will provide something explaining a blanket effect even if details are left to other series.