Jesus when he was crucified willed his spirit to leave his body.
As far as Mary is concerned Since she is without Original sin how could she die a natural death.
Adam and eve had no original sin pre-fall and yet they were immortal.
God sent “his own Son in the likeness of sinful flesh and for sin [or and as a sin offering]” (Romans 8:3). Jesus, like our Blessed Lady, was conceived without original sin but he voluntarily accepted and took upon himself the penalties pertaining to the body consequent to the sin of our first parents such as suffering and death. This, Jesus did, to atone for our sins for “the wages of sin is death.” The death of Jesus paid the penalty and ransomed us from eternal death.
“Surely he has borne our griefs
and carried our sorrows;
yet we esteemed him stricken,
smitten by God, and afflicted.
But he was wounded for our transgressions,
he was bruised for our iniquities;
upon him was the chastisement that made us whole,
and with his stripes we are healed.” (Isaiah 53: 4-5).
At baptism, all our sins including original sin are forgiven as well as all the penalty due to our sins and by the gift of sanctifying grace given us in baptism we are made partakers of the divine nature and heirs to heaven. However, in baptism God does not remove from us all the penalties consequent from the sin of our first parents (original sin) such as suffering and death. This new state of our soul after baptism but still with bodily infirmities, I believe, is similar to Jesus being born in the ‘likeness of sinful flesh’ which as I said he voluntarily took upon himself to atone for us as well as to give us an example of patience and virtue in suffering. Now, of all people, our Blessed Lady was most conformed to her divine Son and she is the co-redemptrix of the human race. And since Jesus, though sinless as our Blessed Lady is, took upon himself the infirmities of the body consequent upon original sin, I do not believe Mary would want it otherwise for herself especially as she was singularly and intimately united to her divine Son in the redemption of the human race.