Actually, you misunderstand the history of what happened. Marie Feodorovna was "persuaded" after the abdication to leave to the Crimea for safety. She had no idea when she left Petrograd that she would never return. She packed only for an extended stay in the Yalta area, not to leave Russia forever.
Thank you. Amazing that wasn't thought of considering how bad things got for the family shortly after the abdication , her son arrested and his family in captivity . But even if Marie Feodorovna thought it might be forever, I can't see the glass plates making the cut.( that is , coming along) They were very heavy and would likely break anyway. Besides a large amount of baggage would excite notice that one is fleeing ....perhaps not wise, nor in keeping with Marie's style...The Russian revolutions were careless of people, but very careful with valuable objects and so the hope remains there is more to discover .
Anne, Maria Fedorovna leave to the Crimea from KIEV, not from Petrograd. She let a big part of her things at Anichkov, where she never return after 1916, as far as I remember.