Given the 50/50 odds from the Inmarsat ping, there is the possibility that Uighurs and/or sympathisers had taken over and directed the a/c to some remote strip / landable area with the view to conduct a hostage negotiation with the Chinese regime.
Setting up military radars in the Himalayas looks to be quite a challenge. And likely one could fly below.
Avoiding CFIT would be a serious challenge.
Aircraft have been lost in the Andes above treeline, sometimes for decades. Survivors of one wreck were stuck for weeks until a party succeeded in walking out.