But why? For example in KDE, if Plasma desktop crashes, it restarts itself and everything else is still running just fine. So, minor annoyance to the user, but everything still intact.
Any time something goes boom in Gnome-Shell, in my experience, after a error screen that is as useful as most Windows error messages (as in, not very) you end up back at the login manager and have to start again.
Also I actually don't mind Unity when its working well. But it's a concern to me why someone would build a desktop into a, at times, fragile accelerated environment when instead you could build the desktop itself and then add the compositing integration.