The bottom line is the UK went to war in 1939 because Poland had been invaded. In 1945 Poland was still in an "invaded" state all be it by Russia rather than Germany at that point. So had a sovereign and democratic Poland been restored? No. War aim achieved? No.
The invasion of Poland was the casus belli for Britain and France - a final line in the sand. The aim of the war was to defeat Germany and roll back Hitlers conquests. That aim was achieved. The war absolutely was not conducted with the intention of liberating Poland.