A H100i cools your CPU and that's it. It also still requires fans because ultimately conventional water-cooling and air-cooling work on the same principle of moving heat from the CPU to the air, then using fans to get rid of it.
Case fans are still needed to provide fresh air to the radiator, and all the other components in your case that still are being air-cooled which include GPU, SSD/HDD, RAM, mobo VRM and North/South Bridge.