No... Mithrax was told by the Witness that Korha, Eramis's bodyguard killed her. However, during that same mission... where we find that out and kill Korha, Ikora implies that it's a lie. Trys to tell Mithrax this, at the beginning of the mission... But Mithrax justifies his Vengeance saying the Eliksni NEED this whether it's true or not. Korha stays silent... never confirms the accusations... I think because he couldn't speak. So, yeah... Mithrax was estranged from his Mother... he had no clue of her whereabouts until the Witness lied to him.