Have you considered adding functionality to 'pin' windows or tabs in TO? In other words, the window would remain in the TO tree, until trashed. This would do some of the job of a session manager, with less messing about.
In detail: A window (or tab?) is 'pinned'. It remains in the TO tree until trashed, even if it is not saved in TO and is closed in chrome. The green cross would still unload the window/tabs as now. If it is not pinned, it acts as it does now.
My preference would be that if the window is pinned, and when closed (either in TO or chrome), the tabs currently inside it are all saved.
In the UI, it could be handled as a pin, next to the green cross perhaps.
Customer support service by UserEcho