I have to agree with JB. Sawyer looked ashen when Frank said about being 100 pounds lighter, and he decided to jump out. He looked ashen, no doubt, upon realising that by jumping out he wouldn't be able to leave the "rock" he was so tired of, judging by his earlier reaction when he first got on the chopper, I'd say he really wanted to leave. By jumping off I believe he acted solely to save his friends, rather than to shrink from reponsibilty, which was very noble of him.
If he'd been trying to "jump out" on his responsiblity, then I doubt he'd have said everything to Kate about Clementine, his daughter in Alberque (sp).