Question on a ruling in my WSOP (#8) event

[yaaaflow]

Ethics question:

I had this come up during a cashgame. Game is crazy pineapple, each player has 3 cards, it is played just like holdem, except one card is discarded after the betting round on the flop. The dealer is to make sure each player discards, but players are also responsible for their own cards. I'm in a pot with an old man who has failed to discard or discarded slowly several times previously.

On a flop of KJ4 all clubs, I hold KJx and keep the top 2 pair. There is betting through to the river, when my opponent reveals his hand of Q93, all clubs - he did not discard, but flopped a flush regardless of the cards he kept.

Dealer declares my opponents hand dead.

Should I a) give my opponent the whole pot b) give him half the pot c) give him back the money he invested in the pot or d) keep it all?