Is it permissible to offer expiation for missed days of fasting due to an illness, when it is not known whether recovery is to be hoped for or not?

The one who changes from making up the fast to expiation is the sick person whose recovery is not hoped for. He feeds a poor person for each day instead of fasting. As for the one whose recovery is hoped for, he breaks his fast and makes it up after recovery. To verify whether the illness is likely to be cured or not, one must refer to a specialized doctor to determine this, especially in psychological illnesses that may delude the patient into believing their illness is continuous.