Hi,
it's good puzzle.....i just tried...am not sure about the answer....let's see
Assume Door A is Life Door, Door B is Death Door
If Guard 1 Is the truth speaking guard, he knows his liar companion will always lie, so will tell him the truth and say his companion will ask him to open Door B.
If Guard 2 is the lie speaking guard, he knows his truthful companion will always tell the truth, so will tell him a lie and say his companion will ask him to open Door B.
Since both of them say "Door B" as the answer, it is evident the other door is the correct one. So the prisoner decides to open Door A and comes out alive.