It is my understanding that that is not confirmed.
I could be wrong - most of my recent posts have asked what is actually confirmed and by whom. I feel like people are conflating facts and reports of things that "may" have happened.
IF this is true, and the plane flew for hours under the radar, I would agree with you that it almost certainly rules out hypoxia.
But if this true, and the plane did not fly for hours (also, I am almost positive, UNCONFIRMED), it could have undergone a rapid decompression and plunged into the ocean at that point.
I know you didnt offer up this theory, but its more convenient for me to quote your post, than it is to go back and dig up the original.
If the plane flew for that long at a lower altitude, it would have used much more fuel.
Hopefully someone with some experience (or better math skills than I) can tell us if it still would have been able to reach the target zone indicated by the satellite pings, if it had consumed the extra fuel needed to fly at a low altitude for a long stretch.
Also, can someone provide a link that says that an aircraft only has to descend to 12 000 ft to escape modern radar systems?