I think VODT will be just fine without Peter and Susan. For most fans of the books, you'll find that VODT is their favorite. I think it's going to be great!
As of last week, PC's world-wide total was at $377 million. I don't think PC will reach the same financial totals as LWW, but it should definitely get to the $400 mark. Not really a flop, but I agree that the release date was all wrong. Disney has even admitted as much.