The easiest way to get back the shut down-button in a few seconds is this:
a right mouse click the task bar at the bottom, 2 options will appear, >preferences<, and >about<. Choose >preferences<, then >applets<, then the red circled >shut down<-button, and confirm. That's it! Next time you reboot the original button or buttons will all be there again, instead of the red one, which you can reinstall each time again whenever you should need it.
There are buttons with a similar name, like the green circled >logout<, or the also red circled >quit-logout applet<, just take a look and choose which one suits you.
I never needed any of it, except the >shut down< which seems to please itself in disappearing mysteriously sometimes. But here is the solution to restore peace of mind!
You may also install the nice wheather applet, or terminal-applet on the way!