It's unfortunate that you encountered the bug that makes villagers vanish. That's one bug that will certainly be fixed when the update to Village Sim is released. It usually happens when you drag a villager around after you've been playing long enough that villagers have died. There is no way to get your Golden Child back, but if you'll read the topic at the top of the forum, "Help on the last three puzzles," you'll see how to get help on that last puzzle.