[shmaster]

There is an interesting revelation made in this manga

Spoiler for final volume:

The missing mail world is actually a world the deviated the original fate due to Layfon's mere presence as the only entity outside the fate. And apparently within the memory that Derbonait sealed inside herself, contains the entire script of the original fate (aka Chrome Shell novels), she actually lived after the Duridana fight and sided with Layfon believing he is the only one that can make a difference. Weirsenheim didn't appear after Leva either. Since the final battle with Weirsenheim didn't start, Glendan didn't do anything in the end and Saya continues to sleep.