Originally Posted by
Iscah
The shards are kind of sort of the practical effect of a multiverse if left to themselves, but at the same time they're physically linked to each other within a larger single timeline – and since we also have timeline shenanigans going on, it can get confusing if you think of the shards as timelines as well.
Specifically, the timeline split caused by the events of Shadowbringers has affected the larger timeline that contains the Source, the First and all the other shards together, creating a sequence of events where both worlds are saved together instead of being rejoined and destroyed/damaged.