Knightmare Chess: another question about Chaos, Knightmare, & Think Again

[Laddie]

All 3 of these canceling cards say that if my opponent used a card, he may take it back. But suppose that my opponent chooses not to take his card back:

1. Is the card simply discarded without effect? Or, if it was a card unrelated to the board state (like Second Sight), would it still take its effect, since my opponent declined to take it back?
2. Having declined to retrieve his first card, can my opponent then play a DIFFERENT card on that same turn? Or is he precluded from doing so, having already "played" the first (canceled) card?

I'm well aware that a player is only allowed to "play" one card per turn, but I wasn't entirely sure if a canceled (and subsequently abandoned) card still counts as "played." After all, the FAQ technically does allow for two card plays on a single turn in the following situation: when my played card is canceled by Knightmare and I do take it back in hand, I am allowed to play a second card that turn. So, in that case at least, the original canceled card does not count as "played". Is the same true if I choose not to take my card back in hand?

Help is greatly appreciated. :)