Sorry for intervening, but IMHO much depends on a kind of a mission. Recall U2 Francis Gary Powers: though he was shot down (being on a spy mission) during a very tense period (psychopathic Khruschev, and also KGB were very spiteful at that time), the end of the story was rather happy for him. It seemed he even did not suffer physically too much because shortly after his return to US he became a test pilot for Lockheed. So, he was right not use a poison he was supplied with.
I assume however that if it were a bomber mission, he would better swallow this medicine in the air.