Throwing some idea snippets for the GO3 Finale into the round (based on the things we saw so far).
What if in this scene Azi confesses his feelings but its also a goodbye?
Like the book of life is gone and now things are disappearing (and I guess people too?).
Azi and Crow are investigating, trying to fix everything, having their little adventure to repair their friendship again BUT even if they stop the source, the world is basically riddled with holes now.
And after stopping the second apocalypse Heaven + Hell probably still want to bash each others heads in and put the people on Earth in danger.
Again and again and again. Till one side wins.
Crowley is right, Azi can't change anything.
He can't change the minds of angels and demons and he can't stop the apocalypse.
So they've come to a decision
to reset/rewrite the timeline with a combined miracle and let go of this one. Nothing lasts forever, right? So Azi confesses his feelings, they have a heart to heart talking about the things they always wanted to say to the other because they both knew everything will be different as soon as they do the miracle.
Will they exist in this new timeline? Will they know each other?
When the new timeline happens all the people that disappeared are back. The world is back to normal, except there are no angels and demons, no Apocalypse and no supernatural powers anymore (exept maybe for God herself).
We see familiar faces again like Michael, Uriel, Sandalphon, Dagon etc. all being humans, not knowing they were once angels/demons.
And somewhere there is s little bookshop, owned by a kind, grey haired middle-aged man who welcomes another man with black outfit and red hair (not hellish red but natural ginger color).
This is where the story ends. Either with them meeting for the first time as humans and leaving it open-ended OR (a much better idea from a lovely person on Insta) it is a timeskip and they already found each other again, living a happy married life.
Maybe this is human Crowley picking up his husband and they drive back to their cottage. Maybe it even ends with the shot of the tree with A+C and a heart written on it.
This way we have the cottage and garden ending (it starts, as it will end, in a garden).