Lots of questions still be to be answered. September did not die after all, and does this mean that the Eterrnal Bald Observers (as I've been calling them) are truly eternal - timeless to the point of being invulnerable to any kind of death? Thus would put them in a category even more eternal than the Elves of Lord of the Rings, which would be eternal indeed.
And what of September's statement to Olivia that he could not prevent her death? And what of the alternate reality with Fauxlivia and real Petter's real baby? And there's still David Robert Jones, who seems at war with everyone (but I'm thinking may be in league with other the Bald Observers, who are now out to get September).
But I'll take this 3/4 season happy ending anyway - they're few and far between on television, and they make whatever threat Olivia still faces all the more trenchant.
... Fringe 4.2: Better and Worse Selves ... Fringe 4.3: Sanity and Son ... Fringe 4.4: Peter's Back, Ectoplasm, and McLuhan ... Fringe 4.5: Double Return ... Fringe 4.6: Time Slips ... Fringe 4.7: The Invisible Man ... Fringe 4.8: The Ramifications of Transformed Alternate Realities ... Fringe 4.9: Elizabeth ... Fringe 4.10: Deceit and Future Vision ... Fringe 4.11: Alternate Astrid ... Fringe 4.12: Double Westfield / Single Olivia ... Fringe 4.13: Tea and Telepathy ... Fringe 4.14: Palimpsest