Hi David-
Thanks for the interesting question, I’m sorry for the frustration of losing your save button, that would make me nervous about losing my work too.
Two thoughts come to my head- both would cause the Publish box to actually move below the editing window.
The first possibility is your screen options. There’s an option to change the editing window from two columns to one:
If that’s not the case, then another possibility is that a plugin you’re using, one that displays something in the editor window, is not closing one of its <div> elements, causing the page to interpret it as below the editor instead of on the side. You could test this hypothesis by disabling your plugins, one-by-one, that have anything displayed in your editor window.
Both of these theories would still show your update/publish button below the editor. If it’s disappeared completely, then something else might be interacting with your editor window.
I hope this helps!