The destabilisation of the Rouran from the late 5th century onwards till its fall in the 6th century are often connected to various important phenomena:
the appearance of the Hephtalites, the migration of the Avars, the rise of the Göktürks, the unification of China from the North.
What if the Rouran confederacy had kept going strong for, say, another century or two? What would have been the effects on Iran, Sogdia, China, the ERE etc.?