Hello!
The Moon Keys respawn. There are 2 moon keys total at all times. If one is touched by sunlight or removed from a lock (the oversized keyholes) it disappears and then reappears in the bedroom (p.14) stone chest.
Yes, I agree! I was thinking of adding a "Consecenses" or "What happens if players do nothing" page, but I was too eager to be done and move on to my next project (which surely will have such a page).
Thank you for the input and taking time to comment!