Here is a word of advice, especially for non-pressurized cockpits. Buy a portable oxygen system and use it any time you fly over about 8,000 feet, especially if you are older than about 50. You will feel better when you get there and filling the bottles is a trivial expense.
No idea whether that was an issue in this case. I had a good friend who augered in in his Mooney. They found no evidence of smoke in his lungs even though there was a fire, and determined he died of a coronary event before the crash happened. This is likely what happened here and there could be evidence in his medical records, or not.