Please correct me if I'm wrong...
So all stayed the same to the point of the invasion by the Observers--but without the Observers being there to help Walter. Somehow Walter gets and saves Peter without Peter drowning, all on his own. And with this change, Olivia, Peter, and Etta are safe--but it looks like Peter remembers everything.
And, in the new timeline, Walter exists until 2015, when he suddenly disappears from this timeline.
And Michael is outside all timelines, since the one in which he was created never existed, but he was outside of it before it was changed.
It doesn't make complete sense, but Peter already was existing in a timeline in which he didn't exist before the reset. When Peter stepped into the universe machine and bridged the two universes he disappeared and a new timeline began.
So he was never actually saved by Walter in that timeline and the timeline in which he was saved by Walter had already been erased.
I, uh, am actually following what you're saying. Kinda scary.
TOTALLY OT: I'm watching the Baltimore/New England game. Baltimore is wearing leggings? They can call them whatever they want--those are leggings.