As you might have guessed (or maybe not), my question was merely risen by the mystery of the Opera Ghost, from the Phantom of The Opera written by Gaston Leroux.
I have been all over the internet in order to find if there have been any opera actresses (or any other staff at the opera) reported missing for weeks or even days in Paris in the late 19th century.
I know the characters are based on numerous people but the facts remain true. For example Cristine Daae is thought to be based on Cristine Nilsson. Even though many of Daae's characteristics come from M.lle Nilsson, there are some other singers that Leroux could have been inspired by.
Hence I was wondering if this particular detail was a fiction by Monsieur Leroux, or based on a fact of a random opera actress (or a dancer, or whoever works at an opera in Paris).