Strange, isn't it? Each man's life touches so many other lives. When he isn't around he leaves an awful hole, doesn't he? - Clarence, It's a Wonderful Life
After all that had transpired that night, Sherlock was in a dark place. His secret sister had psychosis, John almost drowned not long after Mary died, Mycroft could have been shot by his hand, and Molly, the woman he now realized he loved, had her heart ripped out of her chest all because of him. He had been so distracted by the emotional turmoil of the phone call that he hadn't realized that Molly was, in fact, with child.
He didn't speak during the helicopter ride back to London. All he kept thinking about was how better off everyone would be if he didn't exist. Victor would still be alive. Eurus wouldn't have been trapped in a prison like Sherrinford. Mycroft wouldn't have to cover his stupid little brother's mistakes. Rosie would still have her mother. John, Greg and Mrs. Hudson would've never been in danger at Moriarty's hand. Hell, Moriarty wouldn't even have had an adversary. Molly wouldn't be in so much pain right now. She would have been married to Tom and had children.
Sure, they had missed him when he faked his death, but would they miss him now after all the mistakes he's made? After all the pain he put them through? He felt that his entire life had been a mistake. They were better off without him.
Mary watched over her Baker Street boys as always. John was a bit shaken, but fine all in all. Sherlock, on the other hand, had thoughts venturing into dark crevices of his mind. Didn't he know how wrong he was? Sherlock had saved John for her, but now she needed to return the favor and save Sherlock from himself.
Author's Note: I have been so excited to share this with y'all, cause It's a Wonderful Life is my fave Christmas movie of all time! I'm just scared that I haven't done it justice. So, please be gentle with your comments if you don't end up liking it.