The AAIB routinely extracts the data (track and altitudes) from handheld GPS units salvaged from aircraft wreckage, but they can't do it if the wreckage is burnt out or sunk to the bottom of the Marianas Trench
I also don't think IFR panel mounts record anything.
I do somewhat disagree with Genghis' suggestion that correct determination of the cause is routine. I have read loads of AAIB reports and I think they are full of holes. On many, if you cut out the "informed speculation", there is actually very little left. I know nothing about accident investigation but I can tell if an investigator (or a solicitor or an accountant) is waffling.
I suppose one could argue it doesn't matter because "we all know" most accidents are pilot error and structural/control failure is very rare, so simply accusing the pilot by default yields the right answer 95% of the time, but that doesn't make it right.
A proper black box which can withstand a fire would make the Mode S debate look like a picnic. They cost five figures plus,
AFAIK, and are quite heavy.