With DJI FPV, you can get a recording of the HD signal in the goggles. It's not as good as a GoPro/action cam footage recorded on board, but infinitely better than what ground-recorded analog FPV footage looks like.

Also possible for the drone to fall into lava and still transmit for a few seconds, maybe enough to get the higher-quality buffer?

Highly unlikely you'd have time to transmit footage. Various chips in the drone would go into thermal shut down at 90 C ish. The lithium battery would probably explode shortly after.

The scene from Terminator II came into my mind!

the appropriate time scale would more likely be milliseconds