Opponent doesn't reveal morphs at end of game

[perm]

Let's say my opponent puts down morphs and wins with it, and then shuffles up and before I can say anything the cards are gone into the deck. What sort of rules would govern this?

[Julian23]

3.2. Game Play Error — Failure to Reveal

Definition

A player forgets to reveal information that he or she has been required to reveal in order to demonstrate that the action taken was legal. If revealing the card was optional, treat the decision (and any resulting infraction) as though the other option was chosen.

Examples
A. A player plays Worldly Tutor and places the card he searched for on top of his library without revealing it.
B. At the end of a game, a player shuffles her morph card back into her library without revealing it.

Philosophy
Failing to reveal a card prevents opponents from verifying that an effect was played correctly. While the error is easy to make, the potential for abuse is high and the DCI wishes to track players who repeatedly commit this infraction. Few of these errors can be caught before the exact information and location of the unrevealed information is lost. If the card was ever in a position to be uniquely identified (such as on top of the player's library or the only card in hand), downgrade this penalty at Competitive REL.

Additional Remedy

If the card is still uniquely identifiable, reveal it to all appropriate players.

Penalty
Game Loss

Source: The Infraction Procedure Guide. (http://www.wizards.com/wpn/Document.aspx?x=Magic_The_Gathering_Infraction_Procedure_Guide)