It depends on your timeline. If you eliminate dissent you may be able to push through short-term aims or develop a facsimile of national unity, but you will naturally eliminate nuance from your geopolitics. Even one or two generations into this experiment, you can wind up with a leader who truly "drinks the koolaid," who assumes the state propaganda to be reality. At that point, the regime is doomed.
There possibbly is no leader in history who drank the state propaganda koolaid as deeply as Chairman Mao. He accidentally murdered tens of millions when the propaganda turned out to be incongruent with reality. Meanwhile he stayed in power by butchering millions of potential opposition members, and by having nukes and ten million soldiers which impressed Nixon enough to bow and scrape before him.
The lesson has been learned by Chairman Xi. As long as he brutally cleans house domestically and is a MAD-level military threat, absolutely no one can doom his regime.
It's the same reason we're seeing so much strife in the US. In the US, societal opinion and legislative action hardly follow the same path. In fact, IIRC, public opinion has almost no impact on legislation. Wonder why everyone here feels like we're going down the wrong track?
Wishful thinking is a temptation, but it doesn't lead to reasonable analysis. Xi is in fine health at the age of 66. His father lived to the ripe age of 88. His mother is still alive, at 93. We can expect him to receive better medical care than they did, since he is leader of China and they spent several decades getting purged, imprisoned, overworked, and starved by the party. If the Chinese people look for a change in leadership, they had best look somewhere besides the calendar.
Besides, if current dystopic trends continue, most of us won't have 40 years to wait for the expiration of our despotic sovereign overlords...
Usually the first thing dictators do is disarm civilians and beef up the military, so the only way out is via a military coup (which usually just trades one regime for an equivalent one). In just 2 decades, North Korea will have had a dictatorship for a century.