I have read multiple studies on ich that will die off after about 11 months. They can only inbreed 16 cycles before the parasite can not free swim and it dies off. Now the reason nobody in the hobby sees this happen is because. You add a coral, you add an invert or a fish during these 11 months that has ich on it that hasn't been in the system. The second you introduce another strain of ich it starts the clock over. Even if the same strain of ich is introduced from another fish, the ich that is in the system will then reproduce. Hope that clears things up. Now the only way one is going to make it those months is if you have very healthy fish that are either in breeding beast mode, or have a very good immune system from feeding well. Otherwise they won't live those 11 months out
I can also say I have never personally seen this happen, but I have read out of university publishings that this is what they found. I would like to think we can trust marine biologists that do this kind of testing for a living! I will see if I can't put a link up to the journal entries on it.