THE AMBLER - Here is the proof you need. Helios crashed a few years back due to lack of pressurisation. The oxygen masks deployed and the pax used them. they last for 12 minutes on the boeing 737. As the aircraft did not make a descent, the oxygen ran out after 12 mins , therefore pax then died due to lack of oxygen at high altitude.. Ryanair pax did not die due to lack of oxygen. therefore in my opinion the masks were fully operational and achieved their purpose which was to keep the pax alive!!
The cabin would have had a strong burning smell due to the oxygen generators heating up creating the chemical oxygen supply. The burning smell is all the dust layers on the surface of the generator, as they are stored in the ceiling compartments and as with anything sat in the one place for a period of time collect dust and skin particles. If there was no smell in the cabin, then i would be inclined to say that they did not function, but as the pax complained of a metalic burning smell, I can safely say that they were activated along with the fact that they are still alive today.