Doctor Who this year will see the return of Osgood, the scarf wearing sciencey-fan UNIT member. Of course she was killed last season, so of course she is returning. Are we tired of death not meaning really dead and gone or is yet another death retcon a good thing?
Plot wise there are ways around this: there’s Osgood’s Zygons duplicate, but that story explained they needed their human duplicates alive. Unless something really needs to change, it would be unnecessarily annoying to undo that complication. Again, it is unlikely, but maybe The Doctor reconstructs her atoms more successfully than those of Elton (Love and Monsters) or Astrid (Voyage of the Damned) to (belatedly) save her life. Or perhaps her ‘better looking’ sister without asthma was actually her twin? If Martha and her ‘cousin’ can be identical, surely sisters can be?
Unless it was all a dream? A dream explained by the later episode Last Christmas. A dream because everyone is stuck with aliens in their heads eating their brains. In his dream, The Doctor brings back The Master as Missy and gives the salute he could never give to the Brigadier in life (tear) and makes Danny Pink the Best Teacher/Soldier in the world, in his second death. Not realising it is a dream, they fall in deeper and end up in the Arctic. Escaping the Arctic dream, they return to what they think is the real world in Dark Water and Death in Heaven, where they find Danny and Osgood are dead and Missy is The Master and not dead.
The trick, a magicians trick, will be required to pull them out of this reality like rabbits out of a hat to save The Doctor and Clara. And just like that, Danny will be alive, and Osgood will be alive and everyone will be really angry and confused and weird because they all thought they were dead or in mourning.
As for the Missy Master, she will either be ‘no more’ and The Doctor will go into therapy or Missy will manifest herself because if any nightmare could escape a mind and become real it would be The Master, wouldn’t it?
Or I’m entirely wrong because dream retcons are the mostly the overplayed lamest retcons and all my premises are false.
In any account, I guess we’ll find out in August.

Plot trajectories in science fiction can go anywhere, but some semblance of internal sense needs to operate to make everything that interacts look like it is meant to be that way. Osgood’s death wasn’t that.