How to log out if the session applet is missing from the top panel?
Solution 1:
Press Alt+F2, type gnome-session-save --logout, then hit enter. If an application is blocking logout, try gnome-session-save --force-logout
Solution 2:
If you enable Ctrl+Alt+Del, you can use that to kill the X server, which will log you out. To enable this, go to System -> Preferences -> Keyboard, then go to the Layouts tab and click Options. Expand the "Key sequence to kill X server" and check the box.