"Cas! CAS!"
His name is seized by the whirling, roaring winds that viciously whip clothes and roughly tousle hair, broken down to individual letters and scattered through a glaringly bright hole ripped in the very fabric of reality, intimidating in its size and intensity. The light that punches through causes everyone looking at it to cry out and force eyelids as shut as they can be, though, when that is obviously not enough, arms are thrown up to prevent instant blindness. He thinks he hears his name screamed out again, louder this time, not that the whirling wind and deafening white noise of the maw he is staring into will allow for other noises. He wants more than anything to look back at the owner of the voice, like he did when faced with a similar portal not so long ago, and yet years too, but he knows that a simple flick of his eyes will shatter his concentration, will make the Enochian stumble on his burning tongue, will bring the whole ritual down around their heads.
And then it won't just be him that is burning, it will be Dean too. It will be Sam. It will be the prophet, Kevin; the mother who shouldn't be there; the young hunter whose name Castiel can't recall.
He feels his borrowed face blister and it takes all of his power to keep himself together. The entity that he is inside the long-since vacated body snarls against the fire's attempts to unravel his vessel; with claws and teeth he holds together a flesh he should never have stolen and, somehow, manages to keep standing. He knows it can't last though, against the full fury of a portal tapped directly into Heaven's gates. He is forced to his knees but he keeps his chanting going. He can only hope that the humans behind him are weathering the storm; that Heaven's rage is directed at him alone and that the family he has chosen instead many years ago is safe. There are no more shouts and rather than worrying, he tries to believe that Dean has retreated from danger. This is foolish, of course. If the white-hot flames now curling around his vessel weren't there, and the hunter's brother surely wasn't holding him back, the angel is convinced that Dean would be trying to run towards him, to pull him away, to save him.
A wry smile ghosts across his scorched features. For some inexplicable reason to him, the mere thought is enough to renew the vigour with which he intones his spell. He thinks he sees... no. No he can't. After an eternity of chanting and withstanding an inferno of light and white fire, surely the gash in reality can't be shrinking. Impossible. But... the winds are quieting, however imperceptibly. The light is fading bit by bit and the flames reduce in size, strength and ferocity. Cas keeps at his spell as his voice swims back into human hearing; a sound that had been lost in the roar before. The portal is the size of a person now, and this is where the plan was intended to go. He feels hands on his blackened trenchcoat and a shout to "go, you son of a bitch, go!". The hands haul him to his feet and push him towards the hole. He wants nothing more than to look once more at the brothers who had taught him everything he had come to know of people, of Earth, of the wonderful Winchesters. He wants nothing more than to look once more at the man who had laughed at him, with him, for him, who had given him pills for a hangover, let him ride shotgun, introduced him to so many facets of the human experience that it was impossible to list them all, angelic as his mind was. And there it is.
The hole shrinks further still and he is pushed again in the centre of his back. Towards the portal. Towards his home. The home of his siblings, his superiors, his enemies, his friends. He clenches already clenched fists, takes a step, selfishly seizes his one last look at the things he is going to miss dreadfully when the gates snap shut, and finishes the spell. The light that replaces the previous one is enough to reduce the entire area to nothing but white. Castiel flings his burnt arms up, covers his wet and stinging eyes, and hunkers down to ride the fallout out.
Hunched on the floor with his coat pooled on the floor around him, and his tie burned almost completely away, he takes the moment to lament the world he will never see again, and the loved ones in it. The thought is so overwhelmingly powerful that, despite the mistakes he made and the people he killed, he feels himself start to cry at the sudden loss of everything he had known. He wonders about his choice as the unfamiliar phenomenon of crying forces tears to track clean marks through soot and char. A hand falls on his shoulder suddenly, and his doubts vanish. He opens his eyes, sees a sky as blue as them, and a man dressed in denim and leather scowling down at him with both immeasurable fury, and unfathomable relief on his face. He is pulled instantly into a crushing hug - one that seems intent on breaking every rib in his chest – and, though he has had little successful experiences of hugging himself, his arms close around Dean, and he returns it. A muffled "stupid bastard" is muttered somewhere close to his head, but another set of arms closes around the two of them. And they stand there like that. A broken little family, of their own making and own choosing, standing in the scorched crater of a gateway to Heaven closed forever, holding one another as though the world were ending. Again.
But Castiel smiles into Dean's shoulder. It is tinged with sadness for the birth-siblings he has closed away for all time, but at the same time, it is full of hope, relief and absolute gratitude because, for him at least, this world is just beginning.