Killing Voldemort does not help much, he can return to live because of the horcruxes. Dumbledore's plan is simple, destroy each of thehorcruxes before facing Voldemort. But to his horror, the magician alsolearns that Harry is a Horcrux. At this point, a part of Trelawney's prophecy begins to make sense: neither can live while the other survives.
When launched the Avada Kedavra curse on Harry in 1998, destroyedVoldemort unknowingly his own horcrux. Harry finally got rid of theconnection he had with Lord of darkness.