What are you even talking about? The Huns do not exist as a separate ethnic group because over centuries they morphed into other ethnic groups. Aryans don't exist either, yet they became other ethnic groups. Celts don't technically exist when the affiliation with "Irish" and "Welsh" are more significant. But none of these populations died out.

I don't think you understand how ethnicities work. The Celts, Aryans, and Huns were not genocided, nor exterminated, nor did they "fade out". Other ethnic groups and civilizations come from them.