Well first of, in a properly managed environment/team there's never a single point of failure... *ahem*... that being said..
The worst I ever did was lose a whole bunch of irreplaceable data because of... things. I can't go into detail on that one. I did have a back plan for this kind of thing, but it was never implemented because my teammates thought it was a waste of time to cover for such a minuscule chance of a screw-up. I guess they didn't know me too well back then :)