To my knowledge, personal pronouns and the noun they represent can be inter-swapped. So both these sentences are correct. (I may be wrong, I'm not sure.)

"Unless she arrives here early, Susan will be fired."

"Unless Susan arrives here early, she will be fired."

However in the case of possessive pronouns is such a rule/ understanding also the same? My question is, simply put, must the noun be in the main clause always and the possessive pronoun in the subordinate clause? Are both iterations correct or is one more popular/grammatical than the other?

"Due to his poor memory, Richard forgot about the appointment."

"Due to Richard's poor memory, he forgot about the appointment."

One proponent suggested to me that the noun must always be in the main clause, since the main clause can stand alone as a sentence. Is this true? Anaphora or cataphora?