You completely do not understand the situation...I am not trying to be offensive...it is just that your understanding is completely "upside down"...

The "gates of hell will not prevail against it" is NOT because the Church is necessary. Understand that..."the church is NOT necessary!" You are taking the view that the Church is necessary. The Church is not necessary to God. God can use whatever means God would like to communicate the message of Jesus Christ. God could use donkeys or hands writing on a wall to convey the message of Jesus. For the most part God has chosen humans to convey the message of Jesus.

The "gates of hell will not prevail against it" is a function of Him who preserves it. "the gates of hell will not prevail..." is a function of the care that Jesus takes for those who believe in Him. The believers are NOT necessary for the movement of the message. That is why Jesus said," I am the Vine and you are the branches." The Vine is necessary...the branches are not...the branches can be replaced.