This won’t happen. But imagine if in series 3 of Sherlock when Sherlock returned. He had(or was wearing) one of John’s jumpers. He’s a little rough yet the jumper is in almost perfect condition. Since he kept something of John for a sense of normality, comfort etc. I kind of like to think that other than holding on to it because he could never let go of their friendship. He used it as a motive during his 3 years away. That in some ways it was of his strongest reminders of what he was fighting for.