It was possible.
First you had to get rid of Chiang Kai-shek in middle of 1940s.
Then you would have a chance to defeat CCP in the civil war.
Without Chiang Kai-Shek or CCP, China would look like today's Hong Kong or Singapore. I don't think the GDP per capital would be as high as these two areas. That would be impossible for a country this size.
That entirely depends on what sort of potential modernization you're discussing; the GMD-lead Nanjing Decade had similar growth rates to post-1979 Dengist China and was showing significant economic growth potential before the outbreak of the Second Sino-Japanese War. Seeing Mao killed off during the war seems somewhat easy, either via a Japanese bombing raid or a disgruntled party member shooting the erstwhile Chairman during a strategy meeting, or have Dai Li order Mao's assassination during one of the strategic lulls in '42 or '43.
The trick with the GMD is to avoid a second civil war after Chiang dies, which I'd argue would be in the mid-1960s from stress or a "heart attack." The warlords were never fully purged out by Chiang during the war, and that did weigh them down considerably during the Civil War. Quite a few warlord troops jumped ship on the GMD the moment that the PLA showed it had the strategic advantage. Once Chiang is gone, Republican China could end up back where it started after the death of Yuan Shikai and the collapse of the Beiyang Government.
It could be harder to return to the full-blown warlord era with two decades of stability after 1945 to grow the economy and build public trust in local institutions. But, I could see a transitory period of maybe 3-5 years where the GMD undergoes a period of rapid government changes and potentially a military coup d'etat lead by one of the wartime generals, maybe Sun Li-jen. Depending on who it was, there could be a slow easing of censorship and media controls before the government transitioned into a model looking more akin to Singapore or pre-2020 Hong Kong.
The major problem with any GMD-lead government is
corruption: Chiang was well known to be in the back pocket of the Shanghai Green Gang and other prewar organized crime syndicates operating in Chinese-controlled Shanghai (Triads, etc.) Many of the local and provincial police forces in the larger eastern cities were paid off by Green Gang and Triad affiliates to look the other way while they openly ran opium dens, heroin rings, and grew opium poppies. Yunnan Province under Long Yun was the largest opium cultivation area on Earth prior to the Japanese-organized opium cultivation scheme in Manchukuo and Inner Mongolia starting in 1939. Yun had his own strong ties to the Green Gang and Hong Kong-affiliated Triads to smuggle Yunnan and Burmese opium out to French Indochina and onward to Marseilles and the major Mediterranean ports for sale to European addicts. That money piled up in Yun's accounts and was used to buy off GMD officials and bribe port security up and down the eastern Chinese seaboard to not inspect outgoing shipments to Saigon and the French Mediterranean.
So, to get to HK or Singapore levels of development, you've got to purge out or quietly eliminate most of that extreme high-level corruption. China has always had some level of bureaucratic corruption and double-dealing, so that is just status quo for the most part. Lower level provincial bureaucrats are going to take bribes (we used to regularly joke when I was living in the PRC seven years ago that someone didn't bribe the right official when our work visas took too long to process). Getting rid of the high level corruption and decoupling Chiang from his checkered past with the Green Gang and Triads is going to be step one towards a GMD-lead prosperous 20th Century China.
So, guys like Long Yun have to be killed off or marginalized to the point where their involvement with opium processing is gone. Then you've got to marginalize the power of the old warlords, either through old age, through increasing amounts of public transparency, or through growth of public trust in institutions. Twenty years of prosperity could give the public ample reason to trust in, or at the very least not
distrust, the intentions of the GMD to let them cash in on the growing postwar prosperity.
In September 1945, China was about at the same place that it was in 1979; shattered after decades of disastrous policy, millions were dead, the economy in shambles, and the country in desperate need of a change in direction and leadership. If the GMD took out the Chairman and the ability of the CPC to do anything other than to sit in Yan'an and preach the virtues of Marxist-Leninism, it's a wide open field for Chiang to let the Chinese people become prosperous.