I addressed how China might be able to adopt an alphabet on another thread with a different topic, and here's an excerpt:
The Chinese language was consistently written in characters, and the writing system is probably the only one in the world still in use that is not an alphabet. This also assisted with cultural assimilation, as invaders were required to learn the characters, which were also closely tied to Chinese culture, in order to create any records . . . Meanwhile, you would have to ensure that at least one of the northern nomadic groups that invaded China during 300-500 adopts an alphabet, possibly taken from states further west, because they realize that writing is important for maintaining a separate identity.
In other words, although nomadic groups from the north would adopt an alphabet before the Han Chinese do, they would eventually transmit the idea to the state(s) that would later be established within China proper. I will also discuss some of the linguistic issues below.
Let's assume China adopted an alphabet, would this lead to a stronger identity of the Chinese languages/dialects? Would China fragment like the Roman world?
It would depend on how the dialects/languages diverged, and whether there are one or multiple alphabets.
Chinese no matter what they say is not one language. It is a group of closely related languages, think the Romances languages. If they go to an alphabet they loose some of their connectivness and also loose the ability to read much of their old writing without translating it
Yes, but most of the dialects/languages began to diverge during or shortly after the Tang dynasty. If a PoD occurs before the dynasty comes to power, then there is a possibility that an alphabetic system could be adopted in a northern region after influence from other states to the west, and then gradually spread over time over most of China proper. The early PoD also means that there are much more syllabic distinctions, instead of the numerous homophones that exist today, whether tonal distinctions are made or not. In terms of connectivity, the situation would probably resemble that of India, where regions generally have different alphabets and distinct literary traditions.
Well the traditional system was quite efficient (though a lot of allegories were involved , and thus memorization), I can say with 3-4 characters compounded characters what it would take a sentence in English to accomplish.
I think you're referring to Literary Chinese, which was probably never a "language," and was usually used to convey the general sense of the idea, most often used in four-character idioms, instead of a direct linguistic representation. This was why even though the spoken language, including grammar, evolved over time and split into various dialects/languages, the written form generally remained the same, with the exception of coining new terms. Although an alphabet could also function in a manner similar to that of Literary Chinese for a while due to tradition, it would probably begin to approximate the spoken form gradually over time. The ATL situation would be similar to how in Europe, the Romance languages were gradually represented by vernacular forms over time, instead of Latin.