Not to excuse FDR in the least, but I think about half the Jews who were on the ship did survive the war. They were sent back to Europe but not to Germany. Those allowed into England were lucky. Those who went to France and other countries were safe for the time being—until the Germans conquered the countries that had allowed them in.
'Of the 620 St. Louis passengers who returned to continental Europe, we determined that eighty-seven were able to emigrate before Germany invaded western Europe on May 10, 1940.
Two hundred fifty-four passengers in Belgium, France, and the Netherlands after that date died during the Holocaust.
Most of these people were murdered in the killing centers of Auschwitz and Sobibór; the rest died in internment camps, in hiding or attempting to evade the Nazis.
Three hundred sixty-five of the 620 passengers who returned to continental Europe survived the war."
All told, that's about 653 out of 907 who survived the war = 72%.