If Voldemort made all the Horcruxes so he can return with the help of those, and Harry is a horcrux made by accident, even though they destroyed all of the Horcruxes, Harry is still alive, so, while Harry lives, isn't there another chanse for Voldemort to come back?
Near the end of Deathly Hallows, Voldemort casts avada kedavra at Harry. This kills the horcrux part of Harry; the killing curse kills the horcrux. Harry survives because the something else takes the curse - Voldemort's fractured soul.
This is essentially the same as killing the diary, the ring, etc.
With the horcrux dead (by Voldemort's own hand), Voldemort has nothing to come back to.