Calder was kicked out of Orgrimmar due to his horrible experimentation, most likely by the new Warchief Garrosh Hellscream , who distrusts the Undead due to his experiences fighting against the Lich King.
Unfortunately the mad quest-giver has been able to find new work in the Southern Barrens, taking advantage of the bloody war between the Alliance and the Horde to harvest new body parts - with the aid of players - his dream is to create an Abomination using said parts and he expresses quite freely that he does not care whether the parts are human or orc (in his own words "parts is parts").
He appears again at the Crucible of Carnage in the Twilight Highlands. This time, he has an upgraded Abomination who he called the Cadaver Collage. The players battle Dalder's "son" in the ring, and at the end of the fight Calder tells the Collage to use his special attack. The Collage begins floating in the air, but is overheated from his special attack and is destroyed in an explosion.
He appears a third time, this time as a hero, helping the players in the battle against Ragnaros's fiery minions at Sethria's Roost.