The terminal definitely closes - I arrived there before it did, checked into First Cabin, and wandered around a bit as things were closing down. If you can't make it to the terminal by 23:30, catch a cab from wherever you do arrive (you might be able to catch a shuttle or train depending on timing) to over to the terminal. The Keikyu Kyuko Bus is also known as the Haneda Airport Express, you can just ask the cab driver to drop you at stop number eight. They should have no problem with it. In fact, if you want, you can say "first cabin" and they will probably know exactly where to take you; it's a fairly popular service.