I do not believe much would be different, look around, how many people are aware of their own mortality on a daily basis? This question reminds me of something I had read dealing with the gift of Prometheus. Aye, we all know he gave man fire, but there was so much more to that fire. From the comfort and protection of fire, man was also given the “gift not to foresee coming doom… No thinking man of action fears the possibility of dying at any moment.” Of course the greater horror than the possiblity of dying at any moment is the certainty of death after 70, 80, how so ever many years. We are certain to die. But we don’t think of it. At least not often.
The gift of Prometheus was not just fire, but blind hope for the future, to look past the inevitablility of death. From day to day many of us forget that we are certain to die with slight reminders hither and thither. Thus I assume that if man were utterly oblivious to his own mortality he would be hardly any different than the modern man.