vanished into thin air

несбыточный (Dude67); растворился в воздухе (Tanya Gesse)

кануть в воду; растаять в воздухе (Everything in Woland's bedroom was as it had been before the ball. ...... the crow, the party vanished into thin air, without bothering to return indoors and walk up ... Alexander Demidov); скрыться из виду; раствориться в воздухе (Tanya Gesse)

Gruzovik

как сквозь землю провалиться

амер.

развеяться как дым (My money gets spent so fast. It seems to vanish into thin air. Val_Ships)

идиом.

исчезнуть без следа (At least four groups of people who were out that night spotted the peculiar sight, which resembled a set of glowing lights that seemingly slowly spun in the sky until vanishing into thin air.