Now that a factual report has been released, we can at least focus on it.
I find the following timing sequence of particular interest.
UTC
1701:43 a/c at 34998ft
1706:43 a/c at 35004ft
1707:56 with over 12 minutes to run to IGARI, crew report level at 350 without previous ATC instruction to report reaching or when level.
1708:02 ATC response instructing to maintain level.
1719:26 8.26nm to IGARI ATC release a/c
1719:30 a/c acknowledges
1720:31 a/c at IGARI
1720:36 MODE S off
1721:13 a/c drops off primary radar, turns left and then right before commencing descent and increasing speed.
It is inconceivable that between 1720:30 and 1721:13, in 73 seconds, a failure of all electronic/electrical systems may have ocurred so as to render all communication systems and life support systems inoperative and yet allow the aircraft to execute two turns before descending and continuing to follow a diversionary routing, towards an area outside all radar coverage.