I had this happen to me this morning. The tile just disappeared and became a blank space on the region map. I looked for a fix but unable to find one. System restart did not work and I had no previous versions or a back-up. Been working on this region for about a year so did not want to have a blank tile on my map, had to do something.
Found a fix. Started a New Region with the exact same layout (this is key), and gave it a name. Save and exit, go to documents, SC4 folder/regions and copy the cities from the old corrupt region. Do Not Copy the corrupted file, config, or region files. I did not know the name of the city that I lost, was only landscaping at the time, it was New City something, so I just deleted all of them with that name. Paste into new region and worked. I lost all the landscaping i had done, but got back all my old cites.
