Co-op games almost never let you off that easy. Not sure if it's in the rulebook but I'd bet dollars to donuts that you push the inevitable card instead (as that essentially replaces all future episode cards).
Right. Our question was more does it bring out cards from previous or subsequent episodes (like Book's does)?
The cards from subsequent episodes aren't available until after you complete the current episode. And cards from the previous episode are in the defeated pile and wouldn't get added again (unless an effect like Books flaw says to).