Do you return wedding gifts if marriage failed under one year?

NO.

Yes, if you save the receipt they can be.

Added: Etiquette only requires that the gifts be returned to the giver if the wedding is called off. If the wedding happens, but the couple ends up splitting within a few weeks, they are under no obligation to return the gifts, but it may be a good gesture, especially in the case of particularly generous gifts. The couple should consider their relationship with the giver, the length of the marriage, and the nature of the gift when deciding whether or not to return it.