I can't help but notice a plot hole in Fate/Grand Order in relation to the lore of space-time in this series.
In Fate/Extella, it went to great lengths to describe the existence of multiple paths, alternate realities stemming from choices made. Each choice creates a new timeline. But somehow, changing the past in Grand Order causes the entire world that Mashu and Protagonist live in to end. By Extella's logic, the changes to the past would not necessarily result in the destruction of their timeline, but rather, the creation of new ones!
HAX! I call hax!