Mao was ready to face total defeat; even at the hands of the Koreans if that were his fate. No matter what, he would fight on to the bitter end.
And then word came. The Sibir decided to wade into the War Against Mongolian Aggression. Old Sarai would fall to them in a matter of days. Maybe this would be enough to save Mao’s fledgling colonies north of Mongolia. Maybe that would be enough to let Chinese forces regroup and even conquer Mongolia. And someday come back in force to Chonqing. And then on to Hanoi... But he knew he shouldn’t get ahead of himself; shouldn’t get lost in dreams of glory. That’s how he got into this mess in the first place.
With the Huns to Kuchum Khan’s West, Mao knew The Sibir would not commit much more to the fight then they already had. But still. Maybe it would be enough. Maybe...
Of Note: The cut off and undefended Chinese colonies.