for what reason did you imagined such a situation? that was what i first thought.
perhaps - if it was my case- i would think that the quality of my relationship with my husband and my mother, would come into question in a life or death situation. this never happened to me. however i think i would let go of resentment momentarily, and have the urge to save both. if i could not save both i would consider, that it was destiny that manifested itself. i could, after feel guilty or not.