What do you think should have happened, if September didn't distract Walternate from finding a cure for lil'Peter ? September said he was supposed to have a kid with Olivia ( let's assume it's Etta ), not Bolivia.
( How does one exclude the other ? Well, you can assume that, if Olivia ever knew Peter had a kid with Bolivia, it would damage their relationship once and for all- or she'd let him go to the other side to raise Henry. With the "reboot", Peter is the only being outside of the Baldies to know Henry ever existed, so she had no reason to be pissed at him, and so Etta came to be. )
So here's what I think could have happened outside of September interference :
Walternate cures Peter, but it doesn't ease Walter and Elizabeth's pain, far from it. So, in a moment of extreme grief, he crosses over to steal Peter anyway. From now on, things are more or less the same that the timeline we've witnessed, BUT with one big difference : since Walter started the cortexiphan trials to bring Peter back home after curing him, if we assume that without September's interference he would have purposedly stolen him, with no intent to return him to the other side, it meansno cortexiphan trials, which means no lil'Olive popping up in Walternate's office. Without that event, Walternate may have never understood who took his son. So, no war of the universes, no Bolivia infiltration, no Henry.
( Of course, that begs the question if it's the Observers as a whole would wanted Olivia to be the mother of Peter's child, or just September ... that makes a big difference, these days ... )