Basically, I would also like an explanation of how the PRC could fall by 1990 at the most, but what Im really interested in what would happen to the PRC after the fall of the regime.
I'm curious about this to.
I don't have any special predictions, but I will raise a couple points that people have brought up in past Tiananmen discussions.
One, people often bring up that, although protests were widespread, they were mostly an urban phenomenon and they never truly threatened the regime.
I think this is true, but understates things. Most revolutions don't truly threaten the destruction of a regime. An Iran '79 type situation -- where the whole governing structure and army just dissolved -- are very rare. In most cases, even severe protests only succeed because of elite defections. Ruling figures and/or the army decide to cast their lot with protesters.
In China, we know that top ruling officials were split. It could easily have been a situation where the leadership decided to make concessions instead of cracking down.
Second, people sometimes argue that even Zhao Ziyang wasn't likely to concede electoral democracy. You'd get a release of dissidents, more rights to free speech, greater personal freedoms, etc. Again, I think this understates things. Reformist leaders might well have hoped to stop short of full democracy, but the flow of these kinds of events is such that concessions and negotiations probably would have led to free elections. You'd see an opening, further protests, and quite quickly things would escalate.
That said, I wouldn't be surprised if a reformist Communist Party, perhaps renamed something like the Socialist Party or the People's Party, were to triumph in free elections afterwards, powered by rural voters.
Beyond that, who knows? I suspect Chinese growth rates would have been lower in the following years, given the difficulties democracies face with forcing through major policies. That said, such growth might have proven more equitable, and something like the Three Gorges Dam might not have been built. Xinjiang and Tibet would probably even more restive. No idea how cross-straight relations would go, or if Hong Kong would be willing to settle for a less autonomous arrangement than OTL. Would N. Korea still survive, or would it at least be forced to liberalize economically if devoid of a Chinese patron?