> That pretty much says everything.
Actually, it says nothing at all as the guy is confused. The session bus and the system bus run in different dbus-daemon instances, so unless both crash (unlikely), either the desktop or systemd is affected, but not both.
Also, I just tried "crashing" the system bus dbus-daemon (the one with the system bus) on my Fedora 18 system with a SIGKILL. Systemd respawned it, I can still log in on the console, the desktop (KDE Plasma 4.9.5) works fine. If dbus-daemon had actually crashed, I probably wouldn't have noticed at all. So sorry, but I'm not impressed. Try harder.