This is how I see the events between Dean disappearing up to the point that Sam hit the dog. A mix of season 3 and season 4 anger and desperation, where he’d lost his brother and might have gone slightly mad. Maybe, just maybe he was going to drive until he found some nice secluded spot and use that nice clean gun and just end it all. Maybe he’d find Dean waiting for him in their heaven. Because living on earth without his brother is worse than being back in Hell.