2017-03-14 : If the creature exiled with Vanish into Memory isn't a creature card (for example, a crewed Vehicle), that card will still be returned to the battlefield, but not as a creature. Since the card returned to the battlefield has no toughness, you discard no cards.

2017-03-14 : If the creature exiled with Vanish into Memory never returns to the battlefield (because it was a token creature, for example), you don't discard any cards.

2017-03-14 : Vanish into Memory cares about the creature's power just before it left the battlefield and its toughness just after it returns to the battlefield. For example, if you target a 2/2 creature with two +1/+1 counters on it, you'll draw four cards, then when it returns to the battlefield without any counters on it, you'll discard two cards.