Even if you did own the destroyed monster (and it was sent to your Graveyard as a result), Michizure wouldn't be usable because it would miss its timing. (The control change happens after the destruction.)
Can this combo well with Horus lvl 4 (control of this face-up card cannot be switched), or Horus lvl 6 (card is unaffected by Spell effects)?
My opponent used mystic box, took my dark magician(only monster on my side) and swapped with her lower atk monster she just summoned(only monster on her side) and then attacked her monster now on my side and ended turn. Is my dark magician still in her control for rest of duel until trap is played or destoyed or do i get it back?