Hahaha, right, I think that the world is ending scenario would be great to add. You can have the character talk a bit of some strange things that happens, so it's another reason to keep the player hooked to the game. Don't give the same story every time, but just give a random story at each game, so the casual player can still come back for just one game because is curious to know some of the weird things that are happening there.
Nice game, I am sure you can complete it nicely. Probably would be played as mobile app too, just make sure that cards are well distinguishable on the small screen. :-)