John Watson sits and waits, for the first month. He sits and waits in a tired chair, as the rain pours down outside, and clenches his cane. He mourns.
After that, he leaves London. There are too many memories attached, too many things to remember about days when you couldn't giggle at a crime scene, where he only had one friend. He sets up a small practice in a quiet village, and he meets Mary.
He heals.
He has children, and gets married, and does everything he ever wanted.
When Sherlock Holmes comes back into his life, he tells him he's not wanted, which isn't the truth, because John is aching for adventure, excitement, a sense of accomplishment and need. But he doesn't say this. And when Sherlock goes gallavanting round with a young woman by his side, both devious and brilliant and perfectly matched, and he is stuck with a pregnant wife and a young daughter and son, playing snap, he can't help but wonder how things would've been.