same thing that happened when Iraq was put together in the aftermath of our Genocide... Our dialects will all converge.
When Iraq was formed, dialects from all the different Assyrian tribes formed into a single one called Iraqi Koine Syriac.
https://en.wikipedia.org/wiki/Koin%C3%A9_language
from the article - "In linguistics, a koin? language is a standard language or dialect that has arisen as a result of contact between two or more mutually intelligible varieties (dialects) of the same language."
From the article "Assyrian Neo-Aramaic" - https://en.wikipedia.org/wiki/Assyrian_Neo-Aramaic#Iraqi_Koine
"Iraqi Koine
During the First World War, many Assyrians living in Ottoman Turkey were forced from their homes, and many of their descendants now live in Iraq. The relocation has led to a separate dialect usually called Iraqi Koine. It is a mixture of the Ashiret dialects (of the above) with General Urmian. Iraqi Koine does not really constitute a new dialect, but an incomplete merger of dialects. Iraqi Koine was developed in the urban areas of Iraq (i.e. Baghdad, Basra, Habbaniya and Kirkuk), which became the meccas for the rural Assyrian population.[34]
This dialect is a compromise between the thicker rural accents of the mountains (i.e. Tyari) and the prestigious dialect of Urmia. Though Koine is more similar to Urmian in terms of manner of articulation, place of articulation and with its consonant cluster formations. By the end of the 1950s, a good number of Assyrians started to speak Iraqi Koine. Today, Iraqi Koine is the predominant use of communication between the majority of the Assyrians.[35]
I'm a proud speaker of Iraqi Koine. XD
To note, the emergence of the Koine didn't mean that the rest of the spoken dialects vanished. The Ashiret dialects were still active because some Assyrians remained in the rural areas and the fact that the first generation speakers who relocated in urban areas still maintained their native dialects. Elements of original Ashiret dialects can still be observed in Iraqi Koine, especially in that of older speakers."
Your question is a legit concern but history already tells us what happens when dialects collide: they simply merge together
For your other question, the national/official language should be a Standardized form of Classical Syriac.
Classical Syriac has the largest and most organized form of any Aramaic language and it's more organized and even modern than our modern dialects.