That resurrection provides a hope-inspiring example doesn't mean it was necessary. If people invented that after the fact, and filled in the details to make it sound even more appealing--or even if it was misleading--but it doesn't interfere with opening one's mind to God, Christianity is still sound. We don't need demonstrations of everything God may or may not have in store for us. It makes for a more compelling and consistent case, but it doesn't sink Christianity if it's wrong, just like Protestants don't seem to have a problem if there is no infallible source of God's will on Earth (but it's a big deal to Catholics).