Is it permissible for a person, if attacked by an armed individual intent on stealing his property, to defend himself, and if this leads to the death of the aggressor, is expiation or blood money incumbent upon him?

If the aggressor is killed under the conditions we mentioned in Fatwa no. 118678, then there is no liability on the killer, neither for retaliation (qisas), nor blood money (diyah), nor expiation (kaffarah), because he is commanded to do so.