Communists will never give up power?

Communists will never give up power! - those words were uttered in 1945 by Władysław Gomułka, the leader of the Polish Workers Party.
With those words, he expressed his faith that the beginning regime of the communist goverment just introduced in Poland on the initiative of and with the help from the Soviet Union would be eternal.
At the time of his speech, the central and eastern parts of the post-war Europe were undergoing political changes which brought a new reality to this corner of the world.
(...) The four countries discussed here - Poland, East Germany, Romania and Yugoslavia - were to become subject to the communist experiment for almost half a century.
Did this experiment take the same course in each of these countries?
Was there one model of communism?
What was the attitude of each of the four countries presented here to the USSR, the cradle of proletariat and the promoter of communist changes in Central and Eastern Europe?
And finally, what were the four different ways of saying farewell to communism and what consequences did they bring?