If everyone stayed healthy, never got ill, never died, could you imagine the population problems that we mortals would have? There's already shortages of some natural resources and that's with disease, crime and natural disasters maintaining population control.
The Bible gives the answer...as it does for life's most difficult questions. I realize this is not the "religious" section, but the question demands an answer from the One who created life and conquered death.
"Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned--"
"But we see him who for a little while was made lower than the angels, namely Jesus, crowned with glory and honor because of the suffering of death, so that by the grace of God he might taste death for everyone. Since therefore the children share in flesh and blood, he himself likewise partook of the same things, that through death he might destroy the one who has the power of death, that is, the devil, and deliver all those who through fear of death were subject to lifelong slavery."
So those who trust Christ as Lord are freed from the power of death; since we were made for eternity; Christ offers to restore our immortality..."the gift of God is eternal life through Jesus Christ"...Who is the Resurrection and the Life. "The last enemy to be destroyed is death." That is the promise of God to those who know Him.