A malfunctioning pilot light would not create a CO problem. More likely it would allow the room to fill with whatever combustible gas the cabin heater would be using. Since it was probably under thermostat control, as the temp in the cabin dropped, the t'stat would've opened the valve to feed the heater, but with no pilot light, the gas would've just kept coming. A CO monitor/alarm would've done you absolutely no good in that case.

CO is a by-product of combustion, and without it, you get no CO build-up. Sounds like what you got was either a propane or a methane (natural gas) flood in your cabin, which came really close to suffocating you all. You would need a low O2 alarm to protect you from that sort of problem. Had any of you lit a match at the time, you probably would've blown the cabin up.