Yesterday my Xfce menu didn't want to disappear, when clicked other window apps, so I've killed it with 'killall xfce4-menu-plugin'. I've logged off my computer. Later on, when I logged in again, I've noticed that there is no Xfce menu. I am using session saving feature of Xfce and was suprised that it didn't restored killed app. I think session saver should remember which apps was added and removed by me to a panel and restore the ones that I've killed manually for reasons another that removing them through panel menu dialog.
No, this isn't the purpose of the session manager. Individual apps need to support session management in order to be saved in the session and restarted next time. Regardless, it's not appropriate to have plugins stored in the session.