China has had major internal violent conflicts many times: in 1967, 1960, 1937, 1916, 1856, and so on. Another civil war probably isn't imminent but based on historical patterns it's entirely possible in our lifetimes. There could be an external shock in terms of a severe disruption in food or energy imports, or an internal power struggle between CCP factions. Xi Jinping isn't immortal and no one can predict what might happen when he leaves power.