If I understand the reference material correctly, hypo won't affect the ich on the fish at all. It only kills the ich after the ich parasite matures and falls off the fish (tomont stage). In other words, the ich on the fish CAN kill the fish, and hypo won't do anything to stop this.
You can reduce the number of parasites on the fish by combining hypo and increasing the temperature of the tank. The increased temp will accelerate the lifecycle of the ich on the fish, thereby causing them to fall off faster. Then the hypo breaks the lifecycle, preventing re-infection.