This "no ammonia = death" is another of the myths that many still tout as "fact." In an article on the subject of nitrifying bacteria (AOB and NOB) in Practical Fishkeeping a few years ago (link below) we read:
Another ‘folk wisdom’ follows that without a continuous food source, AOBs will soon starve, die, and it’s game over. A scout around various forums reveals that the usual time suggested by well-wishers (myself included) hovers at about eight hours before the Nitrosomonas will turn their tiny starved toes up.
Again, the research forces a rethink. It’s noted that Nitrosomans europa can be starved for weeks or months, and then when placed in ideal conditions (in this case experimental ones, admittedly) regain their abilities to oxidise ammonia within just a few minutes. Older studies put forward a more lingering timescale before reactivity, over 150 hours before oxidising is properly resumed, but the fact remains that the AOBs are bouncing back from hardship.
But, and it is a but that can’t be ignored, there is more to this than may meet the eye. Although the recovery of single cells can be rapid, an entire population may take somewhat longer to emerge. And autotrophs are notoriously slow at ‘dividing and conquering’.
Different Nitrosomonas bacterial strains reactivated at different rates, and what seems to have some consistency is the longer the time in starvation, the longer the time for recovery.
The rest of the article explodes other myths about these bacteria. One thing to note, is that specific conditions (temperature, pH, etc) can impact all of this too.
www.practicalfishkeeping.co.uk