We'd all be better informed if there was a simple switch to activate "VOX" (voice activated transmit) for 121.5 MHz, so at least everybody would have heard the cockpit conversation as it went down without any further pilot interaction.
I wonder if safety people have ever considered such a concept. (If VHF comms used SSB instead of AM interference would be much less of an issue for using such a technique.) They might even suggest actuating this mode automatically on AP disconnect until the pilots turn it back off. Then 121.5 MHz becomes our surrogate CVR.