Mark Gatiss refused to reveal if this meant the death of John's wife, Mary, which did happened in the original stories:
"Just because it’s in the stories doesn’t mean it’ll happen in the series because there’s an awful lot of changes and an awful lot of places to go and things to do," he said, adding: "It should be clear by now that while, of course, Doyle is our absolute god, we have gone quite a long way away as well — we’ve introduced Sherlock and Mycroft’s parents [for instance], I don’t think they’ve ever been seen in any adaptation — so there are lots of surprises to come.”
A special Sherlock episode will begin filming in January with an airdate later in the year. A fourth season will shoot late next year with an airdate in 2016.
I'm actually more worried for Molly. Prayer secret for her.