To disable the log out function, set the /apps/panel/global/disable_log_out key to true.
When you disable the log out function, the following items are removed from the panels:
Log Out user menu item from the Main Menu.
Log Out menu item from the Add to Panel -> Actions menu.
Log Out user
menu item from the Actions menu in the Menu
Bar
panel application.
Also, any Log Out buttons on panels are disabled.