I think the reunification of China is very likely. It’s not super uncommon for there to be fairly lengthy periods of disunity before unification in Chinese history. Nothing about the Jin vs Song setup before the Mongols showed up was unprecedented I would say.
Eventually either the Jin would win and we would get a Qing dynasty a few hundred years ahead of schedule. Or the Song (or a Song successor state) could win. The latter is definitely more interesting in the number of ways that could play out, although the thought of the Jin patronizing Song inventors and the technologies created by them could make them fairly different from OTL Qing.