the first day of battle from thousands of missiles smashing your infrastructure to piece
You are assuming that Poland and other EE countries would not know about the impending doomsday until 10 minutes before the mayhem. Any such threat and Russia would gladly offer protection - for a price, of course. Hello, the USSR ver. 2. This time with Poland as one of the republics and without much opposition from the Poles.
Bottom line: I would trust Russia more than the US as a guarantor of Poland's survival.