thats one of the big catches of most semi-realistic space travel sci-fi.. every huge trip is a one way trip, and that being the case... most trips, by the time they are undertaken, there is no need for them back at the origin point, or it's already too late for them to help..
in other words, if every trip is a one way trip, then those one way trips would have to be imperative, and permanent. i.e. colonization.
The main reason we'll keep pressing into space in the next 100 years will probably be industry or manufacturing. I think those things would be so much cheaper to do in z gravity, especially with robotics doing the bulk of the work..