Complex sentence: Khamenei at the time did not have the credentials to succeed Khomeini and Khomeini had already designated another more qualified successor, hence Khamenei at the time was not even considered as a possiblity.
Split into simpler sentences: Khamenei at the time did not have the credentials to succeed Khomeini and Khomeini had already designated another more qualified successor. Hence Khamenei, at the time, was not even considered as a possiblity.