I don't think I'm going to word this thought coherently but it keeps coming back to rattle around in my brain so I think I have to try, and this thought is: Good Omens TV season 3 could have been so, so good and had such a satisfying ending if they'd just ballsed up and canonized a multiverse.
I'm half convinced they were trying to make it a multiverse too, but they tried to be too coy about it and ended up with it ~left up to viewer interpretation~ which in this case really, really didn't work for them. Yes, I know the GO God famously never answers questions, but GO is also famously about dealing with the world as it is and not trying to start it over better again. One of those things has to break, and I think God's characterization would have been a better one to crack than the actual core of the story.
Just. Thematically, the idea that the entire world gets erased and started over doesn't jive with the previous iterations of the story. But it can be made to work, with one extra little bit of detail: there are other worlds. There are infinite worlds. The Trousers of Time are well and truly legging it, and every decision you make creates another you, elsewhere, who makes a different one. Free will has no true meaning, in the end, because even though you can make choices - the paths you do not take are still taken by another you, somewhere else.
There is already a Book Of Life, telling the story of everything that ever has or will happen. Give us God-As-The-Author - not just of this book, but of all of them, for every universe. Every possible sequence of events, everything that can happen, and must therefore happen somewhere.
Why create a world only to destroy it? It's a thing that can happen, and therefore it must. And, elsewhere, there's a world that isn't destroyed, because that can and must happen, too.
There's a world that was ended by Adam at the airbase. There's a world where Gabriel and Beelzebub got everyone killed over a misunderstanding when they tried to run away. There's a world where everything was destroyed when Michael burned the Book, because no pages were saved. And now there will be two more worlds, one where everything is brought back, just the way it was, and one where it all ends, here and now, after this conversation. And it's up to you, little angel and demon, to decide which one you want to be yours, because another version of you will make the other choice, and both will be as real as each other.
With this information, Crowley and Aziraphale’s choice isn't about erasing everything and starting over, it's about beginning something new. It's saying: No. Let there be a third choice. One world that you bring back, one that you end - and let that be ours, we are ready for it - and one that you never touch. One world where free will is real, where choices have meaning, where when you make a decision, you have to live with it, because there is no other you to make a different one. One universe, free from the ineffablity of the multiverse, that exists wholly and entirely on its own.
And the show still ends the same way. Anthony and Asa exist, and meet, because when it comes down to it Aziraphale and Crowley are God's favorite blorbos and there was no way they were making a universe without them, but they are the only versions of themselves who ever exist, and every choice they make is a real one - no other chances, no other universes where they can live a different life.
The Aziraphale and Crowley we have been following are gone. But, in a universe a little to the left, there's another them who chose to have everything brought back, and are continuing their lives in blissful retirement. Slightly beyond that is a world where Michael never got their hands on the Book in the first place, and beyond that there's one where Aziraphale was never an Archangel, and beyond that the original novel universe lives, and the radio play, and the musical, and all the fanfiction... each just as real, and as true a universe as the last. Everything has to happen somewhere, after all.
And in the end credits, we peek into these other universes, just briefly, and see our angel and demon finding each other, time after time.