Ich is not necessarily a death sentance.
There is the school of thought that ich resides in our tanks and in certain fish at all times. Stress from whatever source (other fish, water quality, food issues etc...) can lower the fish's ability to resist the ich that is inside of the fish and it triggers the normally "dormant" ich into an outbreak on that fish which then becomes a visable issue. How it is treated from there is up to you. Some say hypo salinity, other say garlic-y food, and some even say just regular quarantine with some meds, whatever you poison is, there are many
"cures" to ich.
The other say there are ways to permenantly stamp it out and fix it. Usually through hypo salinity for weeks on end in QT while the lifecycle of any remnants die off in your display tank.
This is one of those topics that I don't think we fully understand yet, and without a full understanding comes the inability to recomend a proper "cure" or "treatment". All we have are a grab bag of things that people have tried and had varying sucess with, but as with everything in this hobby we have to take other peoples results with a grain of salt. What worked for them might not work for us. When someone says X-treatment doesn't work, how do we know they did it properly? What is properly? It is hard to tell to say the least lol, and there are a million variables.