The Fall

In a reality where Cas has rewritten history so none of his mistakes post- Dean Winchester exist, everyone is relatively happy. Dean is not in hell, Sam, Bobby, Ellen and Jo are alive, Heaven is fixed (for heaven anyway) and the apocalypse, the leviathan and everything else didn’t happen.
Castiel is now human thanks to the spell needed to create this reality, he is also alone. In saving Dean’s happiness, he had to lose his best friend and give up heaven all over again. He’s ok though, he has a job, he has an apartment, he’s good. Or that’s what he tells himself until Dean strolls into town.
Turns out fate isn’t quite as easy to change as they always thought.