Tactical withdrawal

So the Apocalypse battle did not go as planned. In a bittersweet moment on turn 1, One of our opponents rolled a 6 to penetrate my already damaged Stormlord. He proceeded to roll a torrent of 6's ending in a cataclysmic explosion which took out 2 chimeras, a sentinel, 20 guard, and 15 orks. My brother, who had forgotten part of his army at home, was down to 2 units of grots at the end of the game. I had lost 2 Chosen, 2 defilers a Stormlord, most of the Baneblade (immobilised and missing both main cannon and demolisher), 1 unit of Noise Marines, and a Demon Prince. My ally was in a shoot out, Guard on Guard, inside a ruined city. We had no way of taking and holding objectives so we called it at the Fourth turn. Some changes to my strategy and army composition are in order, but for their first run....not too shabby. In addition, the Doomsday device preformed well and was the focus of much fun. I just dread the day when it goes off and takes half my army with it.