Hm. That raises the question: Does Mongolia align with the Soviets after declaring independence after Beiyang falls? And if so, do they do so as Communists (kinda doubt this) or as nebulously leftist nationalists like in Sinkiang during its period of being under Soviet influence?
fasquardon
As
yoursworstnightmare said the whole thing was already ongoing even before Baron Ungern come to Mongolia in the autumn of 1920's.
After XU Shuzeng occupied Khuree, there was formed several underground organization. Two of them merged in January, 1920 and formed Mongolian People's Party (future Communist party of Mongolia, ironically they didn't think themselves that way). In July they reached Irkutsk then visited Moskow. Soviets initially promised to provide money and weapons as well as train troops. However they were initially not promised direct military help. This all happened before Baron Ungern.
When Mongolian's started so called 1921's revolution (actually it was movement to free Mongolia from Chinese and White Russians) they first freed Kyakhta which was occupied by Chinese. During Communist Era, this battle was greatly glorified and as a kid I believed only 400 mongolian troops defeated 10K chinese troops. However later historians claimed that first Russian artillery attacked Chinese position from its border. After Chinese defense became chaotic due to artillery attacks, Mongolian troops attacked and claimed victory. Some historians also speculate that there was many Russian troops dressed as Mongolians.
Soviets already messed in Mongolia even before Baron Ungern, so if Xu Shuzeng is forced to retreat due to fall of Beyang Government then scenario will go same as above.
So end result is same as OTL.
Moreover it wasn't only Ungern come to Mongolia. There was many retreating White Russians came to Mongolia through Western border as well as Northern Border. So basically White Russians would have come to Mongolia regardless of Baron Ungern.