Q: What is the ruling for breaking the fast due to illness or fear of death?
A: It is not permissible for the ill to break their fast if they are suffering from a condition that is not negatively impacted by fasting.
If, however, they fear or are informed by a trustworthy Muslim, that fasting in their condition will cause them harm, i.e. increase their illness or delay recovery, it is recommended to break their fast.
They are then required to make up the missed days later.
With the availability of this clear concession, if they decide to continue fasting in the face of such hardship, the fast is valid but considered disliked.
If they feared death due to fasting, the fast is also officially disliked. Others, in the school, considered it impermissible.
Source: Kashshaf al-Qina’ & al-Insaf