Hard for me to see it happening right now when both armies have been reduced to just scraps. And what would they be promoted for, escaping Riboku's cage?
Shin and Mouten didn’t achieve much last arc. They shouldn’t be promoted I think. They don’t deserve it from their last performance. Shin hasn’t displayed full fledged decision making capabilities controlling even short scale conflicts until now. We need to see more before he becomes a general handling 30k plus army
They should be promoted precisely
because they survived Ri Boku's cage. Surviving that trap was a feat in and of itself - one worthy of recognition even by the man who trapped them. That's without even getting into the fact they still achieved their objective partially (for a time) in seizing Gian.
There will undoubtedly be a full debrief when they get back to Qin and HQ will of course realise this defeat was on Kan Ki, and that Shin and Mou Ten did good in surviving and bringing back the core of their units.
Also, beyond merit, they should be promoted as a matter of necessity. Qin lost 170K troops with at least 4 generals KIA, including Kan Ki, and another 2 MIA. Either the Q3 (and perhaps newly minted generals in Kyou Kai, Ai Sen and Riku Sen) will have to step up to more responsibility, or Qin has to find better generals to replace them - which is pretty much impossible with Tou and Mou Bu keeping Wei and Chu in check respectively.
Promotions aren't just earned here, they make sense and are necessary for the war effort.