They still exist, the Ossetians are the last speakers of their language, and they seem to thrieve. Of course if you wish for them to survive on large scale, you need them to become the dominating steppe people, the easiest way to do that, are either to avoid the Huns, which was the beginning of the easten steppes people invasions to the west, or you need to make a large group of Sarmatians replace the Turks in Central Asia, so they becomes the primary vassals of the Mongols. So a large scale migration to Central Asia are needed. So if we make the Ostrogoths stronger so they drive the Sarmatians/Alans out of northen Caucasus and into Central Asia.