As we know, Sherlock Holmes and John Watson solved their last mystery in January of 2017 in the episode entitled 'The Final Problem', but that does not mean that these two characters have been fired forever.
To date we have received all kinds of information and, although we should not create expectations about their future, the truth is that the BBC series is not canceled. Does that mean I could return in the future?
Moffat still valued the possibility of a new season, as he told Digital Spy. "I've been busy with 'Doctor Who' and Mark has been doing other things, so we've had time to sit down and discuss what we would do with a new season," he said at the time. Cumberbatch has expressed his desire to return to embody the detective, yes, in an old version of the character. The actor has insisted that although the fourth season is the last for now, would be willing to continue revisiting 'Sherlock'.