The third option is the correct one: enslaved persons would rather die than go back to being enslaved.
By analyzing the excerpt, some phrases clearly show such an opinion. First, the author claims that re-establishing slavery would be impossible. This already sets the mood and the idea that freed enslaved persons are not willing to go back to being enslaved. Second, he claims that the enslaved now "know how to face dangers (...)" and that they "(...) shall know how to brave death to maintain [liberty]". These statements show that freed enslaved are aware of what they have done to earn their freedom and are willing to risk their lives to continue being freemen.