“We know very, very clearly what stories we’re doing. Where each episode goes, what the shattering, emotionally draining, you’ll never be the same again and you’ll never stop crying cliffhangers will be.” - Stephen Moffat
"And I do think our plan is devastating. We’ve practically reduced our cast to tears telling them the plan … we’re probably more excited that we’ve ever been about Sherlock .”
"While we play fast and loose with the original stories, we generally follow the trajectory of what Conan Doyle did. So [John] gets married, and then Mary dies – so at some point presumably she’ll die." - Martin Freeman
In a Telegraph interview earlier this year Martin Freeman spoke about the possibility of killing off his on-screen wife, and he for one seemingly would not be surprised if that does end up happening.
"And that's a Golden Wrap on Mary," -Amanda Abbington
The use of the term "golden wrap," which can be used to describe a special farewell from the cast and crew when an actor delivers their final performance.
A lot of people are speculating that the tragedy that Moffat speaks of will arrive in the form of the death of Mary Watson.
Mary Watson doesn't make any other appearances in the Conan Doyle stories. Her name crops up in conversation during a few of the stories but there's no significant mention of her until The Adventure of the Empty House (adapted in Sherlock as S03E01 - The Empty Hearse). This short story is set after Sherlock supposedly died at the Reichenbach Falls in The Final Problem, three years earlier, and it marks his return. At his point we discover that Watson is now a widower. Sherlock comments briefly on the fact that Mary is dead, but her cause of death is never clarified. Since her date of death is unknown, I estimate they were married for between 2 - 5 years in the books.
But while we assume the 19th-century Mary died of natural causes, Abbington's kick-ass former assassin could well meet her end in a different way. And if and when that happens, there's one bright side for fans... John Waston and Sherlock Holmes back where they belong following Mary's death – having adventures together in their Baker Street flat...
According to canonical chronology, Abbington’s character has already outlived her literary counterpart. In the original stories, Mary Morstan dies sometime during the period between Holmes's apparent death at the Reichenbach Falls and his return three years later, both of which have already taken place in Sherlock BBC.
The modern adaptation has taken creative liberties with the story arch, hinting that Mrs. Watson may have a chance of surviving. Mary and John are about to have a child, and killing off pregnant women isn't a popular twist for this kind of show. Killing her off after the pregnancy would have narrative consequences too, as it would leave John a single father and therefore restricted by this role. Logistically the show may also benefit from having a more central female character in it, especially as Moffat has spoken about the difficult in adapting the "sexist" original stories.
Let's just hope that she has a future to look forward to.