One take I see popping up, among people who thought that Good Omens Season 3 had a righteous ending, is along the lines of "everything had to be annihilated and made over because God's game was rigged, they were never going to save the world as it existed, so their sacrifice was necessary to create a just and fair world in which humanity could have free will."
The logical flaws aside -- why assume the God we're shown in s3 would keep her bargain? How was humanity any freer to choose than in the 6000 year old Good Omens universe, given that choices still have consequences in our world, whether or not a capricious God imposes them? -- I could go on -- none of this Byronic defiance of/bargaining with God fits the narrative we fell in love with.
One of the conspicuous things about Good Omens, the book, and the screenplay thereof, is the absence of God in the proceedings. Her presence as an omniscient narrator obfuscates this, but God's voice-overs actually stand in for a neutral narrator voice in the book (mostly Terry's, from the tone of those passages). After the Flood, when Aziraphale states the Almighty is a bit "tetchy," God doesn't take any direct action. In fact, it's a critical element of the plot that Aziraphale is certain God will listen to reason if only he can speak to Her, but his attempt to reach Her is blocked by the Metatron; we get no assurance that God is even paying attention at this point. Heaven and Hell, certainly, are gung-ho for their cosmic footie match, winner take all. And Heaven seems to have lost its grip on any concept of what "good" actually stands for. That is one of the things the book was satirizing -- the definition of goodness as blind compliance with received authority, with rigid, arbitrary rules and black/white concepts of virtue. Aziraphale and Crowley, the observers who've been embedded with Humans for centuries, have learned that existence is more complex.
Aziraphale brings that home with his rules-lawyering at the airfield. Yes, the War is the Great Plan, but is it the Ineffable plan? The one that is apparently only known to God? Neither Heaven's nor Hell's representative can answer. The whole operation comes to a screeching halt, Gabriel (or the Metatron) and Beelzebub retreat, Adam stands firm when his father appears to thunder at him. Armageddon aborted, it would seem -- and still God, in the words of Porphyria's Lover, has not said a word.
Is God even bothered at this point? Has S/He buggered off somewhere to be Ineffable, leaving everything to representatives who may have drifted further and further off course? Does the Metatron even talk to Her as billed, or has he usurped God's authority, Wormtongue-style? (That would fit with putative manipulations of the Book Of Life.) Is God still set on that six thousand year drop-dead date? Or does She even remember where She put her toys? I think it would be a very Pratchetty thing to find -- perhaps after another Aziraphalean throat-clearing, or perhaps Crowley taking point this time -- that God got distracted, or learned from Her creation, and was receptive to skipping the whole seas turning to blood, last judgment business.
Something like that would harmonize so, so much more with the book that's been loved for thirty-five years and the screenplay made from it. And there would still be Free Will, a sneaker kicking a pebble, a couple in a cottage in the Downs (with full memories of what made them a couple), and humans thrashing it all out, as we've always done.
