It would depend on which branch of communism they decide to follow. The Maoists way (of which Juche seems to be a subshoot of) has led to nothing but death and destruction for its adherents.
But with much more resources avaliable to it, and maybe a 10% military spending budget, it certainly couldnt be worse.
Both you and I are being off-topic. This thread is like an AHC, not an WI.
As for Maoism v. other ways of communism, the Stalinist doctrine of "Industrialisation at any cost" (i.e. the guiding light for Great Leap Forward) brought much, much more death and sufferings than the Cultural Revolution ever could.
Juche thoughts was an attempt by North Korea to rid itself of BOTH Chinese and Soviet influences. The "self-reliance" mentality in Juche-ism actually kick started earlier than the Chinese one, when Mao was still busy putting "anti-soviet" people into prisons.
Personally, I think a unified communist Korea would be more like Vietnam and Yugoslavia: it'll be unorthodox in ideology, like IOTL. But it will also be early to introduce market economy, because with the ROK gone, the west would be forced to deal with the DPRK (which is much desired by the latter as they always need the west to balance out China and Russia).
The current pathetic state the North Koreans are in is not entirely of their own choice. One thing is clear, they certainly wants to trade with the world and loathes the sanctions imposed upon them.
It's not that North Korean leaders do not want to reform. Kim Jong Il, for example, admires Park Chung-Hee's economic achievements. The real hindrance to reform is the fear among the leadership that once North Korea becomes economically and culturally influenced by the South, a South-led unification becomes inevitable. Such fear would not be there in a unified Communist Korea.
A North Korea which could unify whole peninsula would definitely be much more confident than IOTL, and much more daring to reform.