Uldren is 100% alive, and stranded on Mars. Mara was reported dead by one of the few surviving Paladins, but I don't believe she is really. She, Eris, and Osiris were in contact with each other over the problem presented by Oryx since before Skolas's capture. The Coven Leader of the Techeuns knew of a plan, and I don't think Mara would blindly charge into battle with an unknown foe