The Samaritans have always said this was false and that they, the Samaritans, were the descendants of the northern tribes.
Genetic studies have shown that the Samaritans and Judeans have the same genes and this pdf gives more information
Note that The book of Chronicles compounds the difference in interpretation of Samaritan history. Recalling that Hezekiah ruled the southern kingdom of Judea from 715 BCE, after the Assyrian victory, the following passage seems to contradict the above statement from II Kings: And Hezekiah sent to all Israel and Judah and wrote letters also to Ephraim and Manasseh that they should come to the home of the Lord at Jerusalem to keep the Passover.” (II Chronicles 30: 1)
Some of them probably are. Since the Assyrian idolatry after the depopulation event eventually lost out, it’s not surprising. That doesn’t mean they weren’t carried off, and the Assyrian records show that it was true. In addition, the ancestors of the Ashkenazi resettled north of the Black Sea didn’t memorialize Jerusalem, they memorialized Samaria.