When a creature is destroyed as a state-based action, what happens next?

When a creature is destroyed as a state-based action, it is put into its owner's graveyard. This is the default behavior dictated by the rules of Magic: The Gathering regarding what happens when a creature's toughness is reduced to zero or less, or when it is specifically destroyed by an effect.

State-based actions are checked before a player receives priority, and when a creature is deemed to have been destroyed, the game instructs that it must go to the graveyard. This is consistent with the fundamental mechanics of the game, where the graveyard serves as the default resting place for creatures that have been removed from play due to destruction.

In this context, other options are not applicable because they describe different effects or actions that do not occur when a creature is destroyed. For instance, exile refers to a different action that removes a card from the game, and returning a creature to its owner's library or shuffling it in are not standard consequences of destruction. Hence, the correct answer clearly reflects the outcome of a creature being destroyed within the rules of Magic: The Gathering.