"No company is going to announce a departure of a CFO without...

"No company is going to announce a departure of a CFO without announcing the replacement."

With respect, you are wrong about this. An example: on 15 November 2017, ACX announced its CFO was to retire. ACX did not announce his replacement until 23 November 2017.

Another example: on 14 July 2017 IDT announced the resignation of its Managing Director. It has yet to announce a replacement.

Two very different companies with very different fortunes (ACX shareholders now considering a takeover offer from Oracle, IDT deservedly languishing in penny-stock territory) but both saw it important to announce departure of senior execs before selecting a permanent replacement.