Dragonball Z Old enemies return an unexpected twist from the dragonballs

While the battle of super Saiyan Goku and frieza transpires on the dying planet namek, the earth's guardian kami made a wish to shenron the eternal dragon of earth to revive the namekians and all the people killed by frieza and his men. However a small loophole within the wish allowed two old foes of the z-fighters to return to the world of the living. Where will they go from here? Will these threatening foes give up their evil ways or while the earth's defenders are the other side of the galaxy will the earth be doomed?