Trato demoníaco

If there are any cards left in your library as you search, you must choose one of them.

If there are thirteen or fewer cards remaining in your library as this spell begins to resolve, you will exile your entire library. You won't put any cards into your hand.

The thirteen cards remain in exile. That's part of the bargain.

You do not have to reveal the card you find. That's not part of the bargain.