I can see from the answer to "How exactly do onion addresses work" that the tor protocol needs to upload the hidden service descriptor in item 6, to a distributed hash table (DHT). Is it not possible for a government simply to block the nodes in the DHT that are responsible for sharing how to connect to a particular onion server.
Furthermore it appears that the introduction points themselves can be censored. Is it actually possible? And how likely is this scenario?
I won't say that's impossible but it is very unlikely and probably quite difficult. If it were that easy, there would be a lot fewer onion-based markets. Also, as soon as you notice that your site is being censored, all you would need to do is create a new .onion address and they would have to start from the beginning. If they could simply censor an onion server, then they would.
It is more likely that they will try to de-anonymize the onion service due to carelessness on the part of the person running the server. If they can find an IP address associated with the onion service, or if they can find someone talking about how they are running that site online, they will use that instead.
