There is a group who are the surviving Sarmatians/Alans called the Ossetians. But who said Scythians and Sarmatians don't exist today? If you mean purely linguistically, then maybe but otherwise, Scythians/Sarmatians later became Ukrainians, Hungarians(Scythians joined the confederations that gave rise to Hungary), Tatars, Chuvash, Volga Bulgars, Khazars were all Scythian/Sarmatian with Turkic speaking conquerers who later melted into these populations and hence speak Turkic languages.
If you want them to remain linguistically too, then you need to prevent them from being conquered by the Turkic speakers.