The Jiangxi Republic appears, at least on the surface, to be different than the modern People's Republic of China that we know. There is the obvious Soviet influence, internationalist bent, the images of Lenin on the currency, etc. They even seemed more internationalist than the Soviet Union at the time, but whether these are merely attempts at garnering Soviet support or not are unknown.
Is there a way for the Jiangxi Republic to continue existing past the Civil War, or even expand from its initial borders, centered around Ya'an (so they are fairly inland)? I don't see it really surviving the Civil War, at least as we know it, and it would probably evolve into the PRC anyway. Would the Soviet love persist more so if it didn't die? Would the Soviets be willing to co-opt them into their fold?
A good place to start would be avoiding the Long March, and several encirclements.