The Nationalists winning the conventional war would put them in control of the country, with the Communists broken to the extent that they cannot actually take and hold territory.
The problem is... what then?
The Nationalists were, as many have said, essentially a coalition of the urban middle, professional, and commercial classes with the rural landowners, many of whom were barely better than feudal lords. It was clear during the Nanjing Decade that Chiang Kai-Shek was aiming to bring the latter to heel, sooner or later, as his government made real and substantial improvements to governance and infrastructure which favored the former over the latter, as well as investments in industrial and commercial enterprises which did the same. These were ultimately aimed at improving the lot of his urban powerbase such that he could use it to force reforms upon the rural landowners without losing control of the whole ensemble. The problem is that these improvements were largely destroyed during the war against the Japanese, as was the bulk of the Nationalists' combat power, which set any reform program back by at least a decade.
Even working with US aid, the KMT would not be able to quickly or easily rebuild its development initiatives and build the strength necessary to force reforms upon one of the two pillars of its support. It would likely take into the late 1950's or early 1960's before they could eye land reform with any reasonable chance of getting it through landowner opposition. Which begs the question... what do they do to keep the countryside from open revolt in the meantime? The CCP has long since transformed itself into a party of the downtrodden rural workers. If the KMT cannot begin improving their lot they'll face a situation much like that faced by the South Vietnamese government IOTL, or the Japanese in China before them, wherein they control and have support from the urban centers and major transportation links between them, and can generally hold the countryside under ordinary circumstances, but a Communist insurgency can, when it concentrates its forces, take places away from them temporarily. This is NOT a recipe for success when it comes to economic development, as South Vietnam proved IOTL.
It's likely that, in the long run, even the landholder class will figure out that they need to give some ground or die, especially since Chiang seems to have realized this even before WWII and begun directing some of his energies and political capital in that direction. However, the road from 1949 to the point where major land reforms take place isn't going to be short, and it won't be pretty. It will take until the 1960's before they can really finish rooting out the Communists from their rural hideouts, and there probably won't be a Chinese economic miracle along the lines of Reform and Opening until little more than a decade before schedule.
On the other hand, by the time the KMT has gotten the security situation under control and is in a position to implement a major program of export-driven economic growth, there will be a substantial and sophisticated urban commercial and professional class which isn't completely entirely a part of the KMT itself, which means that its economic growth over the coming decades it less likely to be quite as corrupt and cronyist as the PRC's has been. That in turn will positively affect its prospects for long-term liberalization and democratization.