Shree Krishna’s body is Divine, eternal and omnipresent. His body is not born like ours is. It is not formed in His mother’s womb. He is already omnipresent in His Divine form, so He just appears. Meaning, He makes Himself visible at one place on the earth. At this time, He still remains omnipresent. When He “leaves” the earth, He doesn’t really go anywhere. He just disappears. His body does not die, and He does not leave it, because He is His Divine body.