It’s a good thing it’s probably never going to happen, because if the Moon hit Earth, it doesn’t look like it would be good news. This neat simulation from YouTuber Max Mayer was made in Universe Sandbox 2, and shows what would happen if the Moon hit Earth head-on.
In the simulation, the impact of the Moon causes Earth to become an uninhabitable ball of molten rock pretty quickly. Each second in the video corresponds to sixty minutes of real time, and it seems to be just a matter of hours until all life on Earth would probably be extinguished after the impact.
While interesting, it’s not entirely accurate and is merely a bit of fun. For one thing, there should be a large chunk of Earth missing where the Moon hit. Consider that the Moon itself was probably formed by the resultant debris blasted out from our planet when a Mars-sized object hit Earth 4.5 billion years ago or so.
Still, it's pretty fun to watch. Check out the simulation below.