User blog comment:Terrerianoob44/noob here need help/@comment-1427209-20130105211717

Something similar happened to me. If your Terraria NPCs don't spawn for like 5 in-game days or more, you might want to make your houses bigger. Sometimes they won't come back to houses they were previously in if they got killed in them. If making the houses bigger doesn't help, demolish them and make new houses in another place nearby. Then, do all the things you would need to do to get each NPC to appear again. For example, if you needed to make the merchant come back, carry at least 50 silver with you. For the Arms dealer, carry a gun. Eventually they should come back.