Denial. First stage of grief.
Mourning for this peaceful existence. Mourning for what could have been. Mourning for this budding , Aziraphale wasn't gone for good. They were about to turn back. Right?
Rampa stared his angel attentively from the Bentley. The elevator doors were already closing, but the demon wasn't giving up hope. His angel was going to turn around. Wouldn't they?
How could he think for a moment that they'd abandon them here and now, after all they'd been through? It just wasn't possible. Halfway there, Aziraphale was going to press the "down" button. That was obvious..