It would be kinda hard for Xiaoping to make a 180 degree turn on his policies (bear in mind he was purged twice for them). Better bet would be to have the Gang of 4 (Continuation of Maoist insanity) succeed more or Hua Guofeng (USSR style industrialization) resist Deng's attempts to overthrow him better.
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).
Now, a lot will depend on the Political stability of China. The main problem with Maoists was not so much their economic policy as their political one and its insane demands on the economy. Hua Guofeng would be much better in that regard. And Politics is another issue where the direction will be crucial - much of Deng's work was not only opening up the economy, but opening up relations with the west. The USSR was another point of Contention - Maoism already decried it as an Imperialist Power, and Deng did not change that. If a conservative leadership moved closer to the USSR, you could see the economy of both countries being somewhat better, with Soviet Technology and Chinese Manpower managing to offset the demands of excess militarization. The effects of that would be immense, to say the least. And the return of Hong Kong/Macao would be heavilly contested - the lease does expire, but the UK/Portugal might not be too happy to hand them over to this China.
But the world would definitely be a less rich place.