I'm pretty sure you can just disable it by unticking it in ccsm, but I'm not sure if that unloads it immediately. I was 'lucky' enough to have unity completely crash on me a few times without crashing compiz, and on at least one occasion it disabled itself completely from ccsm so logging in gave me just a desktop with the gnome-terminal that I always run (for emergencies like that if nothing else).
I'm pretty sure you can just disable it by unticking it in ccsm, but I'm not sure if that unloads it immediately. I was 'lucky' enough to have unity completely crash on me a few times without crashing compiz, and on at least one occasion it disabled itself completely from ccsm so logging in gave me just a desktop with the gnome-terminal that I always run (for emergencies like that if nothing else).