Moonanchu-Satan didn't challenge God to give mankind freedom to rule himself. He challenged God to let himself rule mankind. Satan is the ruler of the world, all kingdoms are under his power.
This statement, if true, emphasizes the fact that human beings are even more at the mercy of spirit beings , like God and Satan.
The question of why do we die usually gets a 'technical' answer, like the ones above. Regardless of whether they are correct or not, the question is prompted by a desire to keep living. If that desire is strong enough we will look beyond our limitations to try and obtain it, aka scientific advances and God. But the desire is the real trigger to that question.