Consequences of a gigantic asteroid impact with the Earth and survival issues are examined and discussed. Three survival scenarios have been analysed, based on the state of the art of the physical involved phenomena, human needs and the capacities and limits of the available technologies. The possible causes of humanity extinction may come from the direct consequences of the impact, linked to the size or the different characteristics of the asteroid. They can also come from the indirect consequences of the impact, such as the struggle for resources, generalized anarchy, or the mental distress of survivors, who no longer find the desire to fight for survival in very difficult conditions. Various parameters have been considered, including the diameter of the asteroid and the location of the impact. Only two scenarios are presented here in detail. In both, the warning time is about ten years before impact, as it could be expected for a long period comet.