Any cards you don't cast will remain exiled.

The cards are exiled face up.

If you cast an instant or sorcery card this way, it will go to your graveyard after it resolves, fails to resolve, or is countered. It won't return to exile.

Exiling all the cards from your library this way won't cause you to lose the game. You'll lose only if you attempt to draw a card from an empty library.

Casting a card this way follows the normal rules for casting the card. You must pay its costs, and you must follow all applicable timing rules. For example, if one of the cards is a creature card, you can cast that card only during your main phase while the stack is empty.