1. There is no single right action.
Not only do people react to slavery differently, people react to freedom differently, and sudden changes in life differently. Even for a single person, things like their mood and the PCs' Charisma scores (or equivalent) are going to shape the initial reaction.
2. The solution space varies with culture.
The solution space of right actions is shaped by one's beliefs regarding freedom, slavery, humanity, personhood, emotions, etc. Different people will give radically different answers when defining that space, and in so doing reveal things about themselves and their beliefs.
Given the above, you should consider what you wish to communicate about the human condition vis-a-vis the reaction of the former slaves to freedom, and then present NPCs that define a cultural space communicating that. You should be at least somewhat prepared for your players to react with something along the lines of "slaves wouldn't act that way". Personally, I use such responses as an opportunity to invite discussion: "Not ever? Why not?", but segueing into philosophical discussion isn't appropriate at all tables.
3. Support for the idea that your space of possible solutions is a function of the work you are presenting:
When presented with the choice to leave with Pike and be free or stay on the planet as a slave, the Girl of the Day decides to stay, because not knowing she is ugly is more important to her than freedom. Since she is a girl the show seems to regard this as a sensible choice. Sexism Ugh.
Jean Valjean veritably thirsts for his freedom. He at first understands parole to mean that he will now be free, and ends up in what is more or less a staring match for the moral high ground with his parole officer over that point. Once freed, he resorts to petty theft and other criminal behavior out of habit, as his time as a slave has beaten away his former sense of nobility (or so he believes).
Joseph gets sold into slavery, and is pretty upset about it. By 'pretty upset' I mean pretty upset, though. Not very upset. He mostly does exactly the same stuff he did before he was a slave only with more money, food, prestige, and power. Then he gets framed for attempted rape and somehow this makes him no longer a slave because instead he's a prisoner in the local dungeon. He reacts by doing exactly the same stuff. Sometime later he's grabbed from the dungeons and plopped in charge of the country. He seems a little happy about that. Not, like, super happy. Just kinda positive. More positive than he was negative about being a slave though. On the whole, less of an emotional experience than seeing his brothers who sold him into slavery again, by like a million times.
Genie is momentarily speechless, and Alladin has to repeat the wish before he believes it. He is then immediately ecstatic, celebrates in his typical fashion, has Alladin order him to do something so he can enjoy saying no, and then immediately embarks on a massive world-touring vacation, with a brief aside for goodbyes.
Conan is permanently mentally stunted due to his time as a slave during his formative years. He clearly makes quite a bit of recovery/development after being freed but this takes years and he's certainly permanently scarred and much of his social ineptitude clearly stems from this past. He doesn't seem to really understand the freedom thing, at least at first.
As regards the advice given, slavery of one sort or another is often an issue in campaigns I run, and the beliefs underlying the way the game presents slavery have been deliberately varied from game to game. I am confident that there is a space of good reactions, rather than a single good reaction, here, and that the space is largely defined by one's real-life beliefs.
