The rudder issue is a dead end. Fixed a long time ago.
This is a loss of control accident. Why is anyones guess. We have had high speed loss of aircraft due to weather, disorientation, loss of instruments, fatal control problems, icing, suicide, computer resets and so on.
No pilots will start an emergency descent because of decompression from 11000 ft, and if you have a fire you don’t point the nose straight down.
My money is on instruments or possibly an explosion that cuts control of the tail. Pure speculation, but that is the only thing we can do at the moment.