Probably less than you think. At least among his peers.
These kinds of "almost took X offline" happen All The Time, its just that most of the time they get caught before it gets too far. Its inevitable that a few will squeak through the nets.
Mistakes can and will happen anywhere we allow them to. If you want to prevent mistakes, write tools to help reduce the "attack surface" (areas where mistakes can be made). Eg Don't want someone to be able to do "sudo reboot" accidentally? Alias reboot to something else. It won't stop hackers but it might help fight fat fingers.
