Yes, there has been death in the Pokémon series. As Silver mentioned, Team Rocket did kill Cubone’s mother in the Kanto region, so murder does happen. Also, in Unova, Alder’s first partner Pokémon was said to have died of an illness. While there has never been any death during a battle, there have definitely been some close calls. During Ash’s battle against Brock, Pikachu was getting crushed by Onix’s Bind. If Ash hadn’t forfeited, Pikachu probably would have been squeezed to death.
So, why do Pokémon faint in battle instead of die?
Mainly because it is a game for children, but also because Satoshi Tajiri disliked the idea of death in video games, saying that you should treat death with respect.