Depends, but unlikely with the help the USSR was able to give the ChiComs in 1945 after taking out the Japanese. The only potential issue is US presence in China after Japan falls and whether Ichi-Go happens, which basically gave the ChiComs total control over the countryside and wrecked the KMT. With that control unless the US wanted to go all in to help the KMT the ChiComs aren't going anywhere given the state the KMT was in as of 1945, but without Soviet help and with the US sticking it's nose in to some degree it is unlikely that Mao has the strength to actually outright win a Civil War, just seize parts of the country and being unable to be dislodged by the weakened KMT.