Sarmatians had R1a haplogroup as Slavic people have. Sarmatians lived at same area as slavic people.

One of most educated person in 18.century in Europe – Matthias Bel wrote that Ruthenians are descendants of Sarmatians and they are practising old faith(PS: he wrote about subcarpatian rus area and its known that in these area there was a lot of old pagan traditions alive until first czechoslovak republic and its also documentated) and preserving original customs.

So Sarmatians dont disappeared ,they are living among us until today ;). Btw name is explained very well in wiki : The Greek name Sarmatai sometimes appears as "Sauromatai", apparently through a folk etymology associating them with lizards (sauros). Suggestions for this association include the Sarmatians' use of reptile-like scale armour and dragon standards.[5]
So we know that sarmatians are named according their armour and now please take a look at pictures.

Sarmatians at Trajan column :

And now look at Kievan rus horse armour

and Body armour