I also beat Krell without finishing the book puzzle (I'm missing some of the books) and I don't think I found whatever the switch on the goddess statue opened, either, since I'm still missing a secret; if it was not the end of the demo anyway, I would probably have also reloaded the game to finish up there, unless chapter 3 let me return immediately. Since it tells you how many secrets are left when you find one, is there a way to check?
There's one more thing that I thought of that is bothering me, which is that if I'm not mistaken, the harpy said that they would capture "the blue-haired ones" (plural) alive and kill the others, but only Lunara has blue hair. Did it intend to capture Darren? Maybe it was actually singular and my brain just filled that in; in my brain, the harpy was talking about both of them, and I didn't think about his actual hair color until later. (I like the inverse color schemes for the two of them, by the way.)