As a (ex? not sure if we disbanded...) member of the Slaver's Union, we did this sort of thing a lot... we were fully aware that blanket powergaming results in blanket powergaming, so we would either A) threaten to gas all of the slaves if people continued to fire on our ship, B) jettison and shoot some of the slaves (if you shoot cargo, it dies. Period.) to show we're serious, C) discuss the implications of this and get people to "let us off" with a fine, or with "liberating" only as many as they could hold, or D) wtfpwning them since we're in frigging Slave Liners. Pilgrims and Fireflies 1, Liberty Gunboats 0...
I've never seen a Slaver RP that they put all of the slaves into stasis cells that would survive explosion of their ship. Ever. You have to be pretty twisted to be a slaver, and the ones that don't enjoy whipping and beating their slaves in transit just for the hell of it realize that being able to negotiate with the lives of the slaves is worth any food costs... and somehow I doubt that stasis cells are less expensive than the measly amount of food and water we give them. If we feed them at all, that is.
Saving some of the slaves, from parts of the wreckage that retained containment for long enough for you to tractor them in? Sure, that's fine (unless we gassed them, anyway). Saying that your dinky little fighter carried 5000 slaves four systems away all by its lonesome? Not bloody likely. Athenian's abolitionists usually played, like us, that you can save as many as you can carry (usually). Ah, good times...
The moral here is to be concerned about it and to not powergame. If your character believes that they'd rather die than be slaves, and that actually matters to him (the Outcasts probably think that too, after all, but they're our second biggest consumers...), then play that way. But if your character is a bleeding heart moral guardian, then they should be trying to save them rather than be okay with 95% of them dying. Paying the slaver to let the slaves off at a Freeport can actually work if you make it worth their while (a gun and a bribe gets you farther than just the gun, after all). Don't abuse game mechanics in either direction, for or against the slaves. Play along, have a good time, and try to make sure that they can at least accept whatever you send back.