Even though this seems quite unusual, the article indicates the Trump Transition team is on top of it. As stated in the article, the leader serves at “the discretion of the President”.If anyone on the Trump team is uncertain of the replacement, they could make sure there is a Trump supporting replacement for him at 12:01:01.
Trump offered to keep him on board until the day was out but he refused the offer and his mission now is to embarrass our POE via a compliant media.