His Last Vow IS Sherlock’s six-month suicide mission
Sherlock is given the fatal 6 month assignment and it’s cut short before it even begins. We all know how HLV ends. But what if this exact same thing happened earlier in the episode, too? According to Mrs Hudson fawning over the idea of a “spring wedding” in TEH and Mary’s wedding invitations in TSOT, it is apparent their wedding took place on May 18th.
Then John and Mary go on their honeymoon and John doesn’t see Sherlock for “about a month”. For the sake of argument, let’s assume John doesn’t see Sherlock until June 18th, one month after the wedding, the day he finds Sherlock back on drugs. That’s the night he gets shot in CAM Tower. The night of Mary’s reveal is a week later, as Sherlock explains to the EMTs that come to pick him up and bring him back to the hospital. So, it is incredibly possible that Sherlock goes back to the hospital on June 25th. Exactly six months before Christmas. So what does that mean?
It means this is Sherlock accepting a six month suicide mission:
while this is Sherlock dying once his time is up: