Kievan Rus',[a][c] also known as Kyivan Rus',[7][8] was the first East Slavic state and, later, an amalgam of principalities[9], in Eastern Europe from the late 9th to the mid-13th century.[10][11] Encompassing a variety of polities and peoples, including East Slavic, Norse,[12][13] and Finnic, it was ruled by the Rurik dynasty, founded by the Varangian prince Rurik.[14] The name was coined by Russian historians in the 19th century to describe the period when Kiev was preeminent. At its greatest extent in the mid-11th century, Kievan Rus' stretched from the White Sea in the north to the Black Sea in the south and from the Carpathian Mountains in the west to the Taman Peninsula in the east,[15][16] uniting the East Slavic tribes.

the Germans would take it back. (It used to be called Koenigsburg).

I think it was, Poland was making noises regarding taking it over. I think it would be absorbed by Poland.

I suspect that any surviving East Prussians are very few and very elderly.