Buzz Aldrin spoke about that when asked at a conference on the 10th anniversary in 1979. Yes they all knew that the odds of survival weren't good at all. Yes they knew about the NASA speech having been prepared but they didn't know exactly what it would say until long after the mission returned. Every Test pilot acknowledges that what he is doing is likely to result in his death, which is why almost all of the Astronauts who were to be mission commanders were former test pilots. The other astronauts came with differing backgrounds but everyone who wishes to become an astronaut is made well aware they can be killed during training let alone on a mission into the most dangerous environment ever attempted.