Os objetos desaparecidos podem ser recuperados?

Não, ou pelo menos não imediatamente.

Caso contrário, depois que Hermione desaparecesse a poção de Harry, eles poderiam ter recuperado. Desta forma, Harry teria evitado um zero.

Em vez disso, parece que ela se arrepende de ter feito algo irreparável (ênfase minha):

At the end of the lesson he scooped some of the potion into a flask, corked it, and took it up to Snape’s desk for marking, feeling that he might at last have scraped an E.

He had just turned away when he heard a smashing noise; Malfoy gave a gleeful yell of laughter. Harry whipped around again. His potion sample lay in pieces on the floor, and Snape was watching him with a look of gloating pleasure.

“Whoops,” he said softly. “Another zero, then, Potter...”

Harry was too incensed to speak. He strode back to his cauldron, intending to fill another flask and force Snape to mark it, but saw to his horror that the rest of the contents had vanished.

“I’m sorry!” said Hermione with her hands over her mouth. “I’m really sorry, Harry, I thought you’d finished, so I cleared up!”

^{Harry Potter and the Order of the Phoenix, chapter 29, “Career advice”}

A Canon indica que um item desaparecido reaparece. Em Ordem da Fênix , Fred e Jorge forçam o capitão de Quadribol da Sonserina Montague a entrar no Gabinete de Fuga (o gabinete que Draco usa em Príncipe Mestiço para obter a Morte Comedores em Hogwarts).

‘Malfoy just docked us all about fifty points,’ said Harry furiously, as they watched several more stones fly upwards from the Gryffindor hour-glass.

‘Yeah, Montague tried to do us during break,’ said George.

‘What do you mean, “tried”?’ said Ron quickly.

‘He never managed to get all the words out,’ said Fred, ‘due to the fact that we forced him head-first into that Vanishing Cabinet on the first floor.’

Hermione looked very shocked.

‘But you’ll get into terrible trouble!’

‘Not until Montague reappears, and that could take weeks, I dunno where we sent him,’ said Fred coolly. ‘Anyway ... we’ve decided we don’t care about getting into trouble any more.’

_{Order of the Phoenix - Chapter twenty-eight, Snape's Worst Memory - Page 552 - Bloomsbury}

Enquanto Harry está recebendo lições de Occlumência de Snape, Draco entra na sala para dizer a Snape, um tanto empolgado, que Montague reapareceu de ter desaparecido, e está enfiado um vaso sanitário em um dos banheiros dos meninos.

‘They’ve found Montague, sir, he’s turned up jammed inside a toilet on the fourth floor.’

‘How did he get in there?’ demanded Snape.

‘I don’t know, sir, he’s a bit confused.’

‘Very well, very well. Potter,’ said Snape, ‘we shall resume this lesson tomorrow evening.’

_{Order of the Phoenix - Chapter twenty-eight, Snape's Worst Memory - page 563 - Bloomsbury}