Just wondering what would the economic/cold war implications of this scenario be for both The PRC and the world at large? Very negative would be my immediate response!
There would be no country to boom "instead" of China - China itself does not monopolize western demand, but rather serves as an assembly point that adds value onto products whose base parts come from elsewhere. It is also a massive consumer market for those very same products that developing economies make. So, you would probably see the same countries boom as in OTL (Asian Tigers, Brazil, East Europe, Russia), but somewhat less due to reduced Demand from China. Especially for Agricultural and Mineral Exporters.
You would definitely not have the happy era of the past 2 decades, with unusually high growth coupled with low inflation. (Less global demand, not as many laborers lowering costs). But you would probably not have the period of stagflation that just started and will continue for a while (Lower Oil and Foodstuffs prices due to MUCH lower demand).
But the world would definitely be a less rich place.
Overall the world and mankind might very well be worse off indeed, especially if China becomes a giant North Korea in this scenario.
To be fair however the cheap products manufactured in China could very well have done elsewhere say in India, South America or even in India if this country opens up earlier than was the case OTL. An indirect consequence might also be more robotisation and automation in the west. Chiefly in order to drive production costs down and also to make up for a potential manpower shortage.
If the West and especially Europe play their cards right they can ensure their permanent economic and political supremacy in such a scenario. Something which could be a desirable outcome from the point of view of some.
The status of Hong Kong would be interesting in such a TL, it won't go back to the PRC at any time so it may either go to the ROC, become independent or better stay a British colony!