Like allways there will be contributory factors. The questions is just if we will ever find out the truth given the time since the accident and the lack of human remains.
He would have known of (and undoubtedly practiced) hammerhead turns to get out of the tightest of spots, and have known about the risks of going IFR in that region if there was cloud at all.
So my bet is on either physical incapacitation or a mechanical major malfunction such as stuck elevators/ailerons etc both PRIOR to the impact.
We lost a great pilot, but he died whilst practicing what he loved..... RIP