the 2 eng driftdown consideration if we lost an engine ...
I haven't seen any active volcanoes in the Urumqi and Tien Shan mountain range, so multiple engine failures from ash ingestion is practically zero. In all my 4-engine flights over several decades and thousands of hours, I have yet to experience multiple engine failure. Reasonable people may be curious as to why you would burden your mind about a 2-eng driftdown in a B744. . . . Are you a cadet pilot?
Note: You can cross the entire mountain range on 3 engines.