you realise that either if it’s John or Sherlock, you love like thousand suns the crossover with the hannibal lecter universe.
Either way the nature of Sherlock itself guide him in cannibalism, either John become like this after being shot in Afganistan, losing his mind but still at the top of his profession.
Like, there obsession would be equal for each other, a bit like the silence of the lamb. Dear dear.
Sherlock comes home for season 3, only to find that John left everyone. Then, he will have to find him again across the country but it will be difficult for him to, because John knows him too much and tried to fool Mycroft in the same time, his traces hard to follow.
In a sens, it would be more easier for him to become a homeless person, travelling across Great Britain in grief. His experience between Sherlock’s homeless network and his own, plus the lack of, well, ” expertize ” for Mycroft will help him to disappear. Being a soldier helps too.
It will be, finally, the searching and kill of Sebastian Moran who is gonna reunit them again.
And Mycroft would have came to 221B, spoke to Mrs.Hudson, sometimes even with Greg Lestrade or Molly, because she would already be there and just wanted to know is brother from the old lady perspective. Because, well, she Mrs.Hudson after all.
(Obviously it will not be it, but it could be a good story to write, somewhere, sometime.)