The crux of the story is doubled: Saskia's disappearance (that is, her abduction by Raymond); and Raymond's invitation to Saskia's lover Rex to 'experience exactly what Saskia experienced, from the point of the kidnapping on.' And Rex accepts his invitation, which leads to his 'vanishing' and death.
In other words, for a man to (desire to) know what a woman knows (that is, to become the Object of Man) leads to his destruction, or so says _The Vanishing_, in its misogyny and homophobia. Maybe the film is a riff on Sartre's _Being and Nothingness_ (e.g. "My original fall is the existence of the Other" and "It is before the Other that I am _guilty_. I am guilty first when beneath the Other's look I experience my alienation and my nakedness as a fall from grace which I must assume. This is the meaning of the famous line from Scripture: 'They knew that they were naked.'..."), meant to be analyzed through Eve Sedgwick's _Between Men_, Lacan, and Zizek (to tarry with the invalid problematic of 'common sense').
Yoshie