Sometimes they do get stuck. If you leave the asteroid and come back then they get put back in their prisons so you can try again. The prisoners will run towards the ship unless it's directly in line with them.
That hole so early on is a bit annoying though - I'll see if I can get rid of it in the editor.
** done in v1.0.1 now. Some of the work on the editor for release has made that so much easier to fix than it was.
Just as a headsup: you never need to rescue the prisoners to get to further asteroids, but to 100% the game there are bits where guiding them the right way is crucial to saving them.