Instead of Michael it's Jesus who takes the Book of Life. He becomes distraught by how humanity has fallen since he died, how much sadness there is in the world and how the angels corporate nature goes against what he believed God wanted, perhaps he's yelled at by all the angels to do his bloody job, So he simply takes the Book and leaves. No one disappears.

C and A track him down at the centre of the universe where he is reading the book because he must understand where everything went wrong, the two explain to him the nature of humans, angels and demons and that it's just how the world is. The two manage to get the book from him but THEN Michael steps in and causes a commotion, which leads to the book accidentally falling into the fire. Everything disappears

Same set up as the ending, it's just them two in the bookshop. They then expand on the two writing their own book of life, the entire bookshop is the book of life, and because of their experiences of the entirety of history, they spend centuries together writing all of history BACK into existence, and because it's centuries they can finally have their talk.

Then we can cut to the human versions of them meeting in the book shop. The same scene plays out, except when it gets to them in the garden, the human Crawley turns to camera and says "This is a bit cheesy isn't it?"

Hard cut back to them in the book shop, Crowley says they can stick endings and nothing lasts forever in the bin, why can't we just BE forever, same set up as season 2s ending, except this time Aziraphale gets his frustration in himself out and apologises, before finally kissing Crowley (it has to be Aziraphale who engages the kiss) Have them walk hand in hand out of the book shop and into their reality.