Slimelung that is "Dying off: 100% dead/cycle" in polluted oxygen due to too few germs are not dying off at the specified rate. In fact, the dying rapidly slows down and tapers off at around 200-300 germs and gets stuck there. There is no indication on the tooltip that more germs are being created, so I would expect them to completely die off within one cycle instead of being left with 200 germs per tile of polluted oxygen.
This may be related to
Release a few slimelung germs into a very dense area of polluted oxygen so that there are too few of them to survive. The "Dying off" effect is triggered but will rapidly slow down, leaving several hundred germs behind that will be "Dying off" forever.