One day, months and months after Sherlock's death, John once again walks past the door concealing Sherlock's empty bedroom in 221b Baker Street, London. He feels the same shock in his chest and the way his body and mind seemingly deflate the way they always do. The energy drains from the top of his head all the way down his torso and limbs and out his feet and hands. He lets out a shaky sigh and closes his eyes for a few seconds before turning his head and continuing his day, as usual.
But today he steps back to stand in front of the door that seemed to be sealing him off from the life he used to live when he wasn't alone. He'd finally and miraculously found someone with whom he could live, and he had been taken away. He looks at that blockade, the one thing with which he had such a struggle all these long, lonely months… And he takes a step towards it.
He runs his hands through his hair and down his face, and he remembers the bliss of living with that truly extraordinary man. He hadn't been extraordinary to John because of his genius and talent, but for the fact that he was his best friend. John takes another step towards the door and slightly lifts his arm. If he fully extends his arm, he would have his hand on the doorknob that he hasn't touched since the worst thing that ever happened to him. He can't move his arm, so he takes a half-step forward and his hand is on the knob.
John remembers the shuffling and other mysterious noises he used to hear from his flatmate at all hours of the night. He remembers the sound of the door opening in the morning and the footsteps coming out for breakfast. He remembers how Sherlock wouldn't even eat sometimes, but would sit with John all the same. He also thinks about how sometimes, as early as four thirty in the morning, he'd hear his companion leave this room to go do… something. Nothing was too great for his work. Except, sometimes, inconveniencing John too much. He usually had lines he wouldn't cross, like making John wake up at ungodly hours if it wasn't absolutely necessary.
John turns the doorknob… and pushes the door open a crack. He can't breathe, and he won't open his eyes. His leg begins to ache. The ache that had been taken away by one man's appearance in his life had also been replaced by the man's disappearance. John leans forward slightly to step into the room. He feels as if he's falling. He breathes in sharply, puts his right foot in the room, and opens his eyes.
He can't believe it. The entire walls and ceiling are completely covered with enormous photographs of his own face. John stands in the doorway, staring at himself, trying to grasp what is surely a hallucination.
"John," says the familiar, deep voice he'd missed so desperately.
John looks over at the bed and sees Sherlock, dear, sweet, tall, pale, analytical, beautiful Sherlock, sitting on the bed with two hedgehogs and an otter. "John," he says more earnestly. "I had to leave… because I was pregnant… We're fathers!" He holds up their furry children with tremendous pride, and John falls into Sherlock's arms and embraces his new family.