Think logically, if there is a huge carcass rotting in there, the ammonia levels will be higher than the nitrification rate can cope, right?... hence the detectable spike!
So when ammonia levels build to a highly toxic level... the tank could crash, which is why a good biological setup with ample populations of bacteria is important to cope with pollution spikes... it happens on a regular daily basis in our reef tanks... microlife dies, pods die, fishes die, corals die but you don't get the same kind of ammonia levels like in the beginning of cycling a tank where bacteria populations are new and still growing.
But if there are massive deaths all at once.... the crash will happen because the typical biological filtration will be overwhelmed... which is why reefing is all about balance between your limited setup and overstocking/overfeeding.
AT