In John 21:21-23, did Jesus predict that John would live until the rapture of the Church?
I believe that John has seen the return of Jesus. In Revelation, and especially in chapter 4, we read an eyewitness view of the rapture of Christians, Heaven, and the coming of Jesus with His Bride to the New Earth. John was not seeing what might happen; he was awake, he was told to watch and he was instructed to write down what he was seeing.
Our Lord knows the end from the beginning. He is outside our time-trapped worldly perceptions. The Book of Revelation is the written record for what will happen because God has shown to John the future.
"Peter seeing him saith to Jesus, Lord, and what shall this man do? Jesus saith unto him, If I will that he tarry till I come, what is that to thee? follow thou me. Then went this saying abroad among the brethren, that that disciple should not die: yet Jesus said not unto him, He shall not die; but, If I will that he tarry till I come, what is that to thee? This is the disciple which testifieth of these things, and wrote these things: and we know that his testimony is true" (John 21:21-23).