Héroe/Heroína y su Villano/a

Sephiroth impaled her through a region of the body that doesn't completely destroy vital organs(at most damage to the liver/large intestine).
Also no blood is lost in the scene so no major blood vessels are damaged.
Her spine was severed at a point where the brain still functions to control the heart and lungs. However, it paralyzes her legs and abdomen(which is why she slumps over).
Due to immense pain and swelling of blood vessels from being impaled, she falls unconscious but she is actually still alive.
When laid to a watery grave, she immediately sinks implying that body muscle tension is disrupting buoyancy(as well all know dead bodies float).
She died from drowning after Cloud put her into the water and she sank to the bottom