What if Sherlock was playing out a game of “what if” and realizing that he was endangering John’s life and future by coming back?
If Sherlock hadn’t reappeared in John’s life:
- John wouldn’t be put in life endangering situations (i.e. being kidnapped and stuffed in a bonfire; bomb on train, etc.), and John would still have a “future with Mary.”
- Sherlock would still be “dead” and not a pressure point that Magnussen could use to get to Mycroft.
- Magnussen wouldn’t have focused his attentions on Sherlock, and by extension, on John and Mary. After all, in order to get to Mycroft, he hones in on his pressure point, Sherlock, whose pressure point is John, whose pressure point is Mary.
- Magnussen wouldn’t have uncovered Mary’s past and threatened John and Mary’s future.
I don’t think the tearful “Be careful what you wish for” scene in “The Empty Hearse” was all an act. Sherlock was not only realizing that John had moved on and that his role in John’s life has changed, but also that he was further endangering John by coming back. His work in faking death, going on the run, spying, and being tortured would all be for naught if John were to die because of him, again.
I think Sherlock is realizing that coming back to John’s life was a mistake, and he was trying to make it right. To keep Mary safe at the cost of losing his freedom (and John), again.
*sobs*