That's why when someone in a show declares a fight to the death, it should be to the mother-loving bitter death. Characters keep coming back and regain even greater strength and all that BS is stale man. It's a sword fight, cut the motherfucker's head off if you have to, but make sure he surely can't stab you in the back some day down the road!
In a show that spends half its time in the afterlife, you can pretty much garauntee to see some dead villain make a comeback eventually. Some living person who dies and then is even more powerful when he shows up in Soul Society.