I really wouldn't call it a Deus Ex Machina, especially when it was stated from the beginning that it was only a matter of time before THAT happened to him, especially with a Servant like Berserker which drains mana incredibly fast.
Remember, this installation of Fate WAS written by Gen Urobuchi. Quite frankly, I expect horrible things to happen to everyone, and for half the cast to fall into despair. (Probably should note I never got around to reading the novels)
