Pessimistic assumption: Voldemort has made advance preparations which will thwart every potential plan of Harry's based on favorable tactical features or potential features of the situation which might reasonably be obvious to him. These include Harry's access to his wand, the Death Eaters' lack of armor enchantments or prepared shields, the destructive magic resonance, the Time-Turner, Harry's other possessions, Harry's glasses, the London portkey, a concealed Patronus from Hermione's revival, or Hermione's potential purposeful assistance. Any attempt to use these things will fail at least once and and will, absent an appropriate counter-strategy, immediately trigger lethal force against Harry.