I imagine the flight back to CDG was rather quiet? I am guessing the return sector is why there was no relevant information on the CVR? If the CVR was actually 'erased' they should be sacked for that alone! The rest is extraordinary, but actively hindering a subsequent investigation would be culpable, and inexcusable.
I find it difficult to comprehend how anyone can fail to 'hear' "Whoop Whoop. Pull up!"