You do what you want. The expression "his descendants would be 'as many as the stars of the sky and the sand of the sea'" is a typical exaggeration you read in the Bible, so it cannot be taken literally. He was looking for them in Israel, not abroad.
The Jews were supposedly in the Sinai for 40 years, most of it one place, more than one million of them according to the Bible, yet they left no trace of their presence there, not even graves. So, something is not kosher here; you take a pick.
To suggest that the 10 tribes of the House of Israel disappeared and "became" Gentiles simply does not correspond to Jesus' mission and purpose on earth.
and what part of I CAME ONLY FOR THE LOST SHEEP OF THE HOUSE OF ISRAEL do you not understand?