Is it obligatory to pay expiation for the days one did not fast in Ramadan due to a dilation and curettage (D&C) procedure performed after the death of a fetus, and is it permissible to pray while the bleeding resulting from it continues?

There is no harm in performing surgery to extract a dead fetus in Ramadan when there is a need. As for the three days you broke your fast after the operation, there is no sin upon you if fasting was difficult for you, and you must make them up after Ramadan. The blood that comes out after the extraction of the fetus is neither menstruation nor postpartum bleeding.