Ich lives in cycles. It will spend some time feeding off the host fish, and then it will detach itself and sink to reproduce and multiply. After it multiplies it will again make and effort to attack your fish, and there will likely be more.
I recommend keeping the Hospital tank ready, because the ich may very well come back with a vengeance.
"To know that we know what we know, and that we do not know what we do not know, that is true knowledge." -Confucius