Not only that but that action figured in significantly during both the Monks three-parter and this finale.
Without those pictures, she isn't able to build a wall around her thoughts/feelings/memories.
Without her ability to build that wall, she doesn't help defeat the Monks or counter the cyber-programming.
The photos played in just fine.
The arc for this series/season reaches almost Lost-style territory where things are introduced and often rarely explained or forgotten.
The entire thing with the Doctor going back in time to interact with her mother kind of quietly disappeared. Missy's imprisonment for 10,000 years ( think that's the number) ... and the people that mandated she stay in that prison were never bought up again.
I even that given how Missy had a concealed blade in her sleeve to her previous incarnation (Simm's Master), she didn't disarm him before letting him go into the list. Given we never see Missy wield the Laser Screwdriver at any point prior to this episode, I'm assuming the the Master's TARDIS and screwdriver were lost at some point.
Even in the Dark Water arc, The Doctor non-chilantly mentions that Missy had a TARDIS but it's never seen. She has vortex manipulators and that's about it.
Whether she is dead ... look at Simm's run as the Master with the 10th Doctor. He was literally embodied in a ring to be ritually regenerated by a bunch of crazies.You can never rule out a character dying in science fiction or comic books.
I still thought Missy's dead was crap. She's clearly capable of being quite literally backstabbing. Why she turned her back on someone equally capable of that level of treachery just seemed like a huge logical pitfall. With how she handled the Daleks and Cybermen with her "fake last second teleport" ... which itself is kind of a rip-off of a Star Trek Deep Space 9 episode that does the same thing.
They left the door open, River Song style, to show the Master being killed but still have the potential to regenerate into another form before Missy. This is totally intentional in order to give future episodes with a new showrunner the opportunity to bring the character back or make a new Master along with a new Doctor/Companion.
I think the cliffhanger and the numerous regeneration fake-outs were overused, utter bullshit. It's kind of an insult to the audience to leave it at a cliffhanger the way they did when they pretty much fake regenerated the Doctor for the last two weeks.
Some of the most respectable qualities of the show is its continuity but it's also one of its pitfalls. You get neat callbacks or vague references or completely ignored plot points that seem to go against what's happening in later episodes.
Going to make an assumption that Capaldi's Doctor was very difficult to write for. Smith and to an extent, Tennett were probably easier to write for and could fit with a wider range of stories. Capaldi, to me, had to be written with a specific set of mannerisms and dialog or it just wouldn't be believable or feel forced.
