Just 'cause the pre-registration deadline is passed doesn't mean you still can't register (you just don't get the pre-reg discount)! It doesn't matter if you're a PC or an NPC; just be sure to let us know if you're coming so that we can plan accordingly!
Related: We'd love to have another NPC or two join the ranks, so if you're on the fence about coming, why not NPC? It's cheap, you get Goblin Stamps, and it's helping out!