Maybe I’m slow on the draw and everyone connected these dots already, or maybe I’ve just realized how important Jim’s arc is to Aziraphale’s decision at the end of season two.
Not only does Aziraphale meet a completely new, kind person in Gabriel without his memories, but when he finally regains them, he doesn’t revert to his cold self. Gabriel is a reformed person, finally having formed his own opinions outside of the strict guise of Heaven.
And Aziraphale finally realizes that even the worst of the angels have the ability to change.
The happy couple being allowed to disappear and live their eternity together is the proof he needs to believe the others may be swayed as well.
And the Metatron’s timing in all of this is horrifically perfect, catching Zira in a vulnerability that has just formed, and pulling him right back into the cycle of abuse.