I know that the idea of Earth being defeated, in the beginning of a interstellar space age, doesn't sit well. We ALL lost? All of us, even with all that cool stuff? Not even conquered by Martians or defeated and enslaved by Ming the Merciless- no, it's TKO, total wipe out. Everything blasted by a crazy amount of ships and even more incoming when the last fighters die at their posts. That's just how that fictional world is set up, and really has no more suspension of disbelief then dragons or elves, ray guns or teleporters. We don't know what state the Gbaba left the place in afterwords either. We do know that Weber loves Kinetic-Energy Weapons (Drop Rocks), so that should be taken into account.
Now as for "didn't" fall, that would mean the innumerable Gbaba were defeated somehow (Word of Weber is they weren't), which leaves non-military solutions. Since it's unlikely that we'd hack them and set Earth up as a Gbaba refueling spot, we're left with some variation of "everyone hides until the endless armada goes away." That would mean a Rebuilding era. Known variations of that idea to look into would include Space Battleship Yamato, Yokohama Kaidashi Kikō, and of course, "The Liberation of Earth" by Will Tenn. The Earth being turned into a war zone implies some sort of scale, that both sides have near-equal footing, and that the attackers will stop when reason, logic, and military strategy says they should. That is not the scenario this time. We don't know of any surviving humans in the Sol system. We don't know of any surviving _fora or fauna_ in the Sol system.
Best "didn't Fall" options would be people who escaped the war and waited in interstellar space, or hid in some underground vault (on Neptune) start rebuilding using a their-modern knowledge base. Possible, barely likely, and oh, wait, that's what Merlin was trying to do with Safehold.

So I think no: while Earth's total, inhumane, defeat isn't an idea we like that's just how it is in Safehold. Merlin's going to ride to the rescue someday. I'm sure he'll bring cloning pods and soft-serve ice cream to the rubble fields of Earth. Assuming Weber ever takes his foot off the breaks and lets the hero team accomplish anything. Sure, they've taken over the world but haven't even scratched the paint on the orbital cannon aimed _down._
If Earth didn't fall, they're in for a heck of a Gilligan's Island revival.