I don’t think he’ll be dead, rather the Kremlin’s actions regarding him suggest they see him as useful. Nadezhdin gets a lot of help from Russian state-sponsored media in getting his name out there. And while he is seemingly willing to criticize Putin and even score some rhetorical hits, he’s also an official politician who can probably be controlled if necessary. I’m not sure whether he’s a witting part of it or not, but I think Putin wants to keep him around to manage the opposition. The legit opposition may also realize this but may support him anyway because they have no other hope.