Not sure if they’re dead but they are unconscious due to oxygen starvation (hypoxia). There is oxygen at that altitude but not enough to sustain consciousness.
Pilots usually spend time in altitude chambers to learn their symptoms of hypoxia so they can recognize it and put on their oxygen masks on before they pass out. But it sneaks up on you. For me it feels like hot flashes at first then I act loopy, like a happy drunk.
I wonder if that aircraft had a depressurization alarm.
“I wonder if that aircraft had a depressurization alarm”
The Citation CE560 has an annunciator system with Master Caution and Master Warning lights. When the cabin altitude exceeds a certain value (that depends on whether the pressurization system is set to normal or high altitude mode), there is a large flashing light right under the glareshield and then an individual Cabin Altitude annunciator light that illuminates.