@Gollum Said
You know as well as I do that if Frodo kills Gollum those poor little bastards get lost in the hills of Emyn Muil and they starve to death.
And that's game over, man. Sauron eventually finds the ring and kills everything.
"even the wisest cannot see all ends"
If smeagol was killed, Sauron would never have known a hobbit had the Ring, leading to all sorts of other chaos.
Also remember that Smeagol, once escaping the goblin caves, followed the company to Laketown and ate some babies. Its possible that if he were dead, a baby which he ate could have instead grown and become a great and powerful leader who would bring about the destruction of Sauron himself...