Probably something like the rich and powerful were replaced by next generation Replicants who aren't limited by the four year life span.
In the first Blade Runner Eldon Tyrell it was originally intended that the Tyrell murdered by Batty would be revealed to be a replicant, and as a result Batty would head up to the next floor, where he would discover the real Tyrell in cryogenic suspension. Sebastian would then explain that a incurable disease struck Tyrell, who had himself frozen until a cure is found. Subsequently Batty would demand that Sebastian awaken him. Two different versions exist with regard to what would have happened next.
In the first, Sebastian would break down and admit that he made an error years earlier and resulted in Tyrell's death and in a rage, Batty kills him. In the second Sebastian reveals that years before (estimated as 2013) a blackout struck the city, and during the approximately forty-five minutes the power was out, Tyrell's life support failed and he died. Again Batty is struck by despair and feeling there is no hope, he kills Sebastian much as he did in the finished film.