I did once, a ways back in the beginning of my RP career. After some unfortunate real life occurrences, the moderating team decided to can the site as a whole. So, they organized a massive lava flood of the valley the game was set in. They wrote the volcanoes erupting and raining down, and everyone else played their characters escaping through a tiny mountain pass or dying. I had about seven/eight there and all of them except two passed on. Most died by liquid fire, one broke his leg while trying to escape and was trampled, and the last got out with his best friend. Though it sucked, it was a great closing, reading through the multiple threads was awesome and I don’t think it could’ve been done any better. 

Since then, haven’t ended anything officially. xD