The authoritarian societies of the past have tended to fail for specific reasons—problems which the regime in Beijing is very carefully avoiding:
1) They were personalist dictatorships that depended upon the vigor of a single despot whose luck eventually ran out.
2) They were stuck in the past, and did not adapt to modern technology. In this category go traditional societies from Spain to Zululand.
3) They went broke because they didn’t understand economics and thought they could create wealth by political fiat. In this category goes the USSR and all its imitators.
4) They got arrogant and blundered into wars they couldn’t win. In this category go Hitler, Mussolini, and Saddam Hussein.
In China’s case, we can rule out #1 and #2 above with ease. Problem #4, of course, refers, from our present vantage point, to the future, as we cannot be absolutely sure they won’t do something stupid militarily. But the evidence appears to weigh against it. Beijing for now appears to be a disciplined player of the game which, while certainly willing to use force (ask Tibet!), isn’t going to romp into strategic catastrophe from sheer excess testosterone.