Today, the real world is so intertwined with the digital world that it may as well be one thing. If an AI decided it wanted more power, and took over every computer on the planet with it's exceptional speed and intelligence (to be clear, I know this isn't possible today, but someday), we could do nothing to stop it, we'd have to just unplug and reset ALL of our technology, literally replacing any digital storage with zeros as to eliminate the infection. I don't think that's possible without billions of people dying in the interim.