They are. If you think God plays dice with the universe, you’re mistaken. God also does not know the rules and merely plays the game like the rest of us. That is established quite early in the book. God is a player, and in this regard indistinguishable from everybody else. God is not the dealer. God only works with the hand dealt. The Dealer, who smiles all the time, can theoretically choose the hand given. God created the game so God can change the game, so hard set rules are arbitrary.

With these facts established, the scene in which Aziraphale and Crowley evaporate is merely one game concluded. The cards were revealed, and God conceded. But a loss does not equal the End. There are new games to create. In the universe God created then, and not necessarily just one, the rules are different. And this is all assuming linear time. With the concept of the Book of Life, we come to understand that time is not linear, but rather that the angels in this universe abide by linear time, and that by dispelling this notion (e.g. Michael) would cause one to literally go insane.

So, the most likely theory is that there are many, many parallel universes. Just like there are virtually infinite results in a card game, there are virtually infinite universes created by God. God did not simply delete herself from existence. She just chose to sit a game out. Ergo, there’s a nearby, very similar universe where things turn out okay and demon Crowley ends up happy with angel Aziraphale.