C'thun's chunk of the Black Empire covered most of modern day Kalimdor southeast towards modern day Pandaria. Yogg's land covered all of modern day Northrend and southeast towards the northern tip of modern day Eastern Kingdoms. While their bodies are indeed merely "mountains of flesh" as Chronicle puts it, their tendrils reach a LONG way.
Even if you call them "dead", they really aren't. Like Y'shaaraj their bodies surely have a lasting effect on the areas they controlled in the Black Empire. C'thun is probably inactive, not dead. I'd imagine and immense amount of Titan blood funneled right to him might change that though.