@leocg I found out how to back up and restore my windows and tabs, by using "Save All Tabs as Speed Dial Folder." I did that and started deleting workspaces.
I ran into a problem. Workspaces apparently requires the existence of at least two workspaces. That's the whole idea of workspaces. So once I get down to two workspaces, there's no option to remove either of them.
So I can't reset workspaces that way.