IMO if the Shun don't succeed in stopping the Qing at the Battle of Shanhai Pass, they are going to collapse. I think you would be much better off having Li Zicheng succeed outside Beijing, with him securing control of northern China but failing to take the south - if what you are aiming for is a split China.
The Manchu at the time were in a rather desperate situation given that their food supply was unable to sustain their population, so if Shanhai Pass turns into a major victory for the Shun then they are going to be in deep shit. They might turn back to Korea for a Third Manchu Invasion, but Shanhai Pass was a pretty all-or-nothing bet at the time so they would probably struggle even then. With the Qing out of the game for the time being you have far more time for the various factions of Han Chinese to consolidate their positions.
The division in the map is unsustainable given that the Shun possess the weakest and poorest territories, lack any sort of legitimacy w/o securing Beijing and are completely exposed to Qing invasion. If the Qing control the northern plains of China, then they are going to secure the rest of northern China as happened IOTL. Further, the Ming were in collapse in the south as well, and the Southern Ming were hardly viewed as having a firm grasp on the Mandate of Heaven - hell, the last Ming Emperor in the north butchered most of his family before hanging himself so it isn't like they are screaming "We are the Son of Heaven!" to the general populace.
If the Qing are stopped by the Shun, the Shun should be able to consolidate the north if given time while the Southern Ming are likely to face rebel claimants who could set up challengers to the mandate of heaven. A Manchu recovery would put pressure on the northern border of the Shun and would thereby limit their ability to march south - setting up for your wished-for divided China.
