What happens when you kill regirock in omega ruby?

In Pokémon Omega Ruby, when you defeat Regirock in battle, it will faint and you will no longer be able to capture it. However, defeating it does not cause it to disappear permanently; you can reset the area by leaving and re-entering the cave, allowing you to encounter and try to catch it again. Make sure to save your game before the battle to avoid losing your chance to catch it.