What is the ruling on one who dies while abstaining from food for a just cause?

It is not permissible for a Muslim to kill themselves by refraining from eating or by any other means that leads to death, for Allah Almighty says: "And do not kill yourselves. Indeed, Allah is ever Merciful to you. And whoever does that in aggression and injustice - then We will drive him into a Fire. And that, for Allah, is easy." Thus, a hunger strike that leads to death or the destruction of an organ is not permissible according to Sharia (definition), and its perpetrator is considered a suicide. As for anything less than that, there is no religious impediment, as it is a refraining from what is permissible.