if all the governments of all the world joint hands together to banned bitcoins ,then only would bitcoin can come to an end.otherwise it is not gonna happen no where soon. because of its decentralization and no technology could beat because it is the first of its kind.
But even if all government makes it illegal they can not decide that it will die. We have darknet and as you mention it is decentralized, meaning no one can take full control over it, unless you buy up all the BTC's there is, see my post above about that.
Best Regards,
They can never really get all bitcoin it is very impossible, and nobody can never buy such amount of bitcoin by himself and you can really never tell if that's gonna happen the possibilities of a bitcoin shut down will never be because of the government, because even if they don't have control over it they can get something from it.