The Mo Yung Family (father and son, Mo Yung Bok and Mo Yung F'uk) ultimately didn't succeed in their dream of restoring the Yin Kingdom because there were simply too many obstacles for them to overcome in their era: the Sius of Khitan, the Deuns of Dali, Hui Juk and Janitor Monk of Shaolin, etc. Moreover, the Khitan Liao Empire, the Northern Sung Dynasty, the Dali Kingdom, the Hsi Hsia Kingdom, and the Tubo Kingdom would have been formidable enemies had it come to war.
Would the Mo Yungs have had more success if they attempted their plan in a different era? What if they tried during the time of LOCH? They'd have to contend with Juchen Jin Empire and the Greats. If they'd tried during the era of ROCH, they would have to contend with Gwok Jing, Yeung Gor, the elder Greats, and the Mongol Empire. In the HSDS, there would be the Ming Cult and the Yuan Dynasty to deal with. In the SPW era, there would be Dung Fong But Bai and others to pose a problem.
Maybe by the Qing Dynasty, there'd be an opening, but firearms were becoming an issue by the Qing Dynasty. The Mo Yungs would need to acquire some.