What is the legal consequence for an agency authorization (Wakala) when the subject matter of the agency is negated?

Primary text

Agency authorization is voided when the principal's action or possession related to the agency ceases to exist. This applies specifically when an agent is authorized to transport a man's wife, sell his slave, or take possession of his house from a specific person, but clear evidence subsequently proves the wife has been divorced, the slave has been freed, or the house has been transferred away from the principal. Since the principal's authority or right concerning the subject matter is nullified, the agency authorization related to it is also nullified.