I really don’t want to get into this with anyone since it is a matter of faith, both in the general sense of today’s Christianity and also faith in the later writings about the beliefs and related stories of long dead Apostles.
We know He is alive for we have met Him and trust the Word He has written to us.
John 10:29 "My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of the Father's hand.
John 17:24 "Father, I desire that they also, whom You have given Me, be with Me where I am, so that they may see My glory which You have given Me, for You loved Me before the foundation of the world.
1Cor 1:18 For the word of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.