Splitting maul handle cracked... is it still usable?
First of all, that is a splitting maul, not an axe.

Secondly, the handle consists of a tough layer of plastic over a core layer of fiberglass. The plastic cushions the fiberglass, and, more importantly, keeps your hands from getting nasty splinters.

Because the strength comes from the core fiberglass center piece, you can still use the maul, but I'd wrap the broken section with a few wraps of duct tape. It will eventually break (depending on how often you miss), but that could take years.

Should you want to remove it, the best way is to cut off the handle with a saw and then use a drill to drill out the epoxy, and get replacement handle kit. This is time consuming, hence my recommendation to use the handle until it actually breaks, as it often becomes easier to remove then.