Sherlock will soon return to the airwaves with a new season for the first time in three years. Fans have been waiting quite a while for the next set of episodes following Sherlock Holmes and John Watson as they solve mysteries and get into various shenanigans in the process. Unfortunately, there's a chance that Season 4 will be the last season of the series. Co-creator Mark Gatiss said this about the potential for a fifth season of Sherlock:
These three [episodes], we've very, very pleased with them. And everybody's very keen to carry on. It's just genuinely difficult to schedule everyone's diaries. It was a nightmare to schedule this season... and that's not going to go away. I mean, the success of Doctor Strange is not going to make Benedict short of work.
Sherlock has proved that it can adapt to just about any wild storyline over the years so far, but it couldn't possibly continue without stars Benedict Cumberbatch and Martin Freeman as Sherlock Holmes and John Watson. Even if all the other pieces and players can fall into place at a given time, a season of Sherlock simply couldn't happen without the leads on board. Mark Gatiss' reveal to TVLine that they already had a hard time getting both actors' schedules synced up for Season 4 could mean that a Season 5 just won't ever come together.
If Benedict Cumberbatch's Doctor Strange had been a flop, the odds of a Sherlock Season 5 would undoubtedly be better. The film was far from a flop, however; Doctor Strange grossed more than $616 million globally. It is officially the most successful single-character movie in the history of the Marvel Cinematic Universe, beating longtime record-hold Iron Man's $585 million. Marvel won't be letting Cumberbatch go any time soon, and he's already slated to appear in Avengers: Infinity War. Cumberbatch seems quite fond of Sherlock, but a BBC series pales in comparison to blockbuster movies in one of the biggest film universes of all time.
Martin Freeman also has a role in the Marvel Cinematic Universe. He first appeared in Captain America: Civil War as Deputy Task Force Commander Everett Ross, and he'll reprise the role in at least Black Panther. Assuming that Ross isn't killed off in Black Panther, Freeman could have a long MCU future as well as Benedict Cumberbatch, not to mention he's often busy with other roles.
Of course, scheduling has been a problem with Sherlock in the past, and the show has always managed to find a way to come back anyway. Benedict Cumberbatch has said that it may be difficult for them to pick up and continue after the Sherlock Season 4 finale, but he also has said that he finds the prospect of never playing Sherlock again to be "galling." For his part, showrunner Steven Moffat believes that the show could go on indefinitely, with everybody coming together every once in a while to put a new batch of episodes together.