I had the same problem. No renderview. I could see everything was working correctly in the script editor. The option to open it in a panel was grayed out. New scene and opening and closing Maya did not help. I read your post and it led me to think mine was also just misplaced on the screen somewhere. I shuffled my monitors in my resolution settings of windows and my renderview popped up right in the center of the screen. frustrating but glad it is back. Thanks