@burnout426 - Thank you for your responses and explanations. I definitely had a different model for what Workspaces were. It's a little weird that when I create a new workspace in a given window, it appears in all my windows (existing and new). I think that's what made me think workspaces were shared across windows.
It is helpful to have method to insure all windows, workspaces, and tabs are retained. I won't be closing any individual Opera windows unless I'm okay with losing all the tabs/workspaces associated with the window.