It's not decentralized. The directory authorities, which hold the current state of the network, are hard-coded into the client software and trusted by all. They are a central point of failure - if a denial of service attack brought them all down for a suitably long period of time, the Tor network would cease to function.
Despite it being unreachable, it will attempt to disassemble the word after the branch/nop rather than recognizing it as data.