The captain has the last say in the air.
On the ground the company has the last say.
Furthermore, the captain is also entrusted by the company with an aircraft in order to generate revenue in a safe as well as cost effective maner.
Landing at MIA, as oposed to MCO (as per FO advice), or better yet continuing to ORD, over what seems to have been a disagreement with the purser, does not sound very cost effective.
Based on the "facts" so far, I seriously doubt that the company will entrust any more of their aircraft to this guy.