Yes, having a rotting carcass in your abode is bad news, even if it's not in the open. All of the bacteria that's feasting on the corpse will be blowing through your damned vents. You know what a corpse smells like? Shit, maybe piss, and this sort of "sweet" pungent scent. I'd call it "sickly sweet". If you smell that, get the fuck out of there until the problem is dealt with. Your landlord should provide you a hotel room for the duration. And if in a few days, suddenly your apartment is swarming with flies.... you'll know for sure that something is dead in that ductwork. I cannot understate how serious this is. This is not like the fake pandemic. This is millennia old wisdom. There are many, many reasons why we naturally find corpses repulsive; primarily because they spread disease. They could have also been carrying a dormant disease, which becomes active when the animal's immune system stopped functioning.