For China, such scenario didn't happen. The reason is simple. Most of high ranking officials need to rise through the rank and need to demonstrate competency before getting promotion. Consequently, for someone to become the highest ranking officials, it would take a few decades. Therefore, their view and political affiliation are pretty clear to the party.
In the early days of reopening, China is more tolerant and allowed many more liberal thinking officials to rise to higher position. You can see that in 80s, 90s, and 00s. But that no longer is the case, as the new cold has started. That is why you see much more conservatives and hardliners come to power. And how they wean out all those liberals, it is pretty easy as there are long records of political views and thinking of officials as they rise through the rank.
So unless Vietnam decides to do nothing and don't wean out any incompetent libertards, what you said it is unlikely to happen without a coup. If a color revolution truly happened, then Vietnam would no longer pose a threat to China as infighting would de-mantle Vietnam's progress and Vietnam would be lucky to end up like Ukraine.
