Although apparently stronger than Cell in this state, Goku told Gohan he could not defeat him because the form drastically reduced speed for offensive power and thus couldn't beat Cell, because "all the power in the world would do no good if you can't even hit the guy". Because of ...
Goku's death was intended to be permanent so that Gohan could replace him as the series' main hero. The story sees the Saiyan sacrifice himself to defeat Cell, and that was supposed to be his final act. However, as history has shown, "Dragon Ball" has ways of resurrecting deceased chara...