Everyday, after working hard on the engine and at the end of night if I see things like that I have in my mind & satisfied with the results, then I save the whole project file to another hard disk. I suggest you to do that too. Of course always you can “save as” a map but I lived a ton of harddisk failures and I’m really serious about it. It only takes less than a minute.
For this map, I hope you’ll recover it.