Dear Gurudev, you say the body is present only for a limited time. Then how could Bhishma Pitamaha (the great Grandsire of the Kauravas and Pandavas in the Mahabharata epic) in the Mahabharata live so long and die at his own will?
Listen, I am not going to be a lawyer for Bhishma, or for any character for that matter. You can sit with a lawyer and an anthropologist and do all the research on these things.
When we were children, we also wondered how a bird can carry some people on its back. We often wondered how could there be a gazebo on top of a bird which is so small.
Usually in mythological paintings and in stories, we have seen or read about a bird carrying a nice and big gazebo on its back, which we in India call a mantap.
But you know, when you go deeper in science, then you will find that even our scientists say that there really were large birds weighing some 300 tons or so.
In the dinosaur age, there were birds which were so huge they were like airplanes. If they were so big, then you can definitely put ten people on top of them. Why ten, even a hundred people could sit on the top of it.
Those birds could always be trained for such acts. All of this is indeed possible.
We should always say that everything is possible.