Crimean Gothic Survival

Using a POD no earlier than the 8th century, what would it take for the Crimean Goths to exist as a sizable majority in modern day Crimea, comparable to the Crimean Tatars?

I reckon a situation where Saint John of Gothia had successfully expelled the Khazars from the region and established a semi-autonomous Gothic kingdom within the Byzantine Empire's sphere. However, this still leaves the question as to what happens to the kingdom after the invasion of the Mongols, Ottomans, and then Russians.
 
Top