Have any commercial airline passengers ever been injured from hypoxia due to a depressurization event?
The passengers on Helios 522 were incapacitated or died due to hypoxia. Those masks in the aircraft only have enough oxygen to sustain the passengers while the plane descends to a safer altitude, or about 12 minutes. Helios 522 was on autopilot at 34,000 feet for 2 and a half hours. The autopsy showed that the passengers were alive at the time of the crash, but it could not determine if they were conscious. The aircraft was unpressurised at an altitude as high as the peak of Everest, the crew were incapacitated, so it follows that the passengers would have been as well, despite the fact that the autopsy showed that they were still alive at the time of the crash.

Now, let's suppose that they had survived the crash. They were hypoxic for 2 hours, which means they would have suffered brain damage and would be suffering with the long term effects of that (Insomnia, amnesia, etc) as well as injuries sustained from the crash itself.