On the original question, I guess we can all just agree to disagree. Houserules are your friend, since we will probably never

get a rules clarification on this.

Maybe there's a space or denizen on the cataclysm board that allows you to remove a terrain card from the game. That'd be great!

Space - highly doubt it. At least from my point of view, as a random component of the game and as a designer of the mechanic (if I were him), (as well as from personal experience) I would consider Terrain Cards to most likely be there for the rest of the game. (Mind, yes, there are of course some effects to remove them, (already - and yes, we will probably get a few more of those cards) but with the whole giant Adventure Deck, it's just very unlikely that they will pop up every time some "crucial" space gets "deleted".)

Since that makes for a whole different game than usual, these Terrain Cards are part of my favorite mechanics of the game.

There's always the golden rule for arguments, if you need it. We have only used it once since the release of the 4th Edition.