You have to remember that in the original timeline, they were never sucked to the future and Fitz never went into cryosleep. Meaning in the original timeline, they would've went to the diner and then went on their way hiding from the authorities. The Zephyr was never taken from the military base by Fitz and Hunter. Fitz and Hunter never learned of the Lighthouse or met Enoch. They also never met up with Robin and her mother. They never came back from the future with the intent of preventing Earth's destruction, so they never would've went to Missouri and caught up with Ruby because they never met Noah after returning to the present. This means the fear dimension never existed in the original timeline. You have to think about what aspects would've stayed the same had events in the present played out without time travel involved. This leads to another thing, or things: The 3 monoliths in the lighthouse. Where did they come from? They existed in the lighthouse regardless of the time travel. Now, go back to what originally caused Earth to go boom. What we know is the first blame on Quake, then Talbot, then Talbot absorbing Quake. But, if they never time traveled with the intent to stop the destruction or the loop, it isn't necessarily Talbot or Quake that caused it. The time travel changed their actions from the original timeline, such as Yo-Yo killing Ruby. Hale going rogue and causing the attack that sparked Talbot getting in the machine was caused by Ruby's death. Next, in the original timeline, who got everyone to the lighthouse? Does the last of humanity in the lighthouse consist of the residents of River's End? Also, They followed tunnels to River's End in the midseason premiere, so where were those tunnels in the future? Was River's End on the part of Earth that was decimated?