RE: The Will to Live as the "on/off" switch of Human Beings
Hmmm.... thinking about this in terms of our future, if we start developing tech for (serious) space travel, I think the first candidates will probably be people who are already doomed to die (terminal patients) / have already lost their will to live, due to the nature of the one-way-trip (it's unlikely that the first trips will be two-way). They'll psychologically compensate this sacrifice with a part of Freudian motivation to write history and leave some kind of legacy - like "first man on Mars".
(Alternatively, scientists will just use AI robots. By 2025+ it'll be possible to eliminate the human component and nobody will need to die. The AI will probably be used to set up colonies so that humans can go and find things already prepared for them.)
If they're already dying, it sounds unlikely they're going to survive for hundreds of years in a can in outer space.
They won't. I think the first space travels will be much more conservative in their targeting, like establishing a base nearby, with a one-way carrier-ship. The technical difficulties involved in getting the crew back, even from distances as close as Mars, are enormous - so they'll probably pick people willing to die (or AI-led robots). For trying to reach earth-like planets, several light years away, that'll probably take centuries indeed - unless they make some wormholes to warp time/space... that could be an option, who knows...