After the destruction of Zerox, most of the survivors (mostly sorcerers) resettled on Tharn.
During the economic collapse of the galaxy (as featured in the v4 Legion of Super-Heroes, Tharn was undefended when threatened by the Khund. To face this menace, the ruling sorcerer's council restored Mordru's power to him. He defeated the Khunds and set himself up as Emperor. The Legion later confronted him when he held a Green Lantern captive, eventually winning his release (though the Lantern's power ring was destroyed).
The planet has not appeared post-Zero Hour.