What if Pontius Pilate decided not to have Jesus crucified and instead locked him away in some dungen for a few years and every one forgot about him, and then Jesus died and was buried in some shallow grave and no one was around to see him reserect if that really happened.
I honestly just don't see how that would have happened. It was standard Roman policy to crucify messianic pretenders. There were probably standing orders in Jerusalem during the Passover, the most nationalist of all Roman pilgrimage festivals, for the pro-Roman Sanhedrin and priesthood to turn over all messianic figures for crucifixion.
Moreover, and I'm not saying this out of Christian conviction or belief in divine providence (though I have both), I think Jesus of Nazareth planned the whole thing. He entered Jerusalem as a triumphal prophet of the kingdom of God, overthrew the temple which was both a symbol of Jewish pride and Roman domination, and even held a formal final supper. Even if he wasn't God, or was God incarnate but had no comprehensive divine omniscience during the earthly ministry, he
must have known he was going to his death.
Maybe he was attempting to rally people into a revolt by placing himself in the role of martyr. Or maybe he was trying to stir Yahweh's wrath when the Roman's kill his anointed prophet. Or maybe he thought he was talking on the exile and shame of Israel on his own shoulders, mano-y-mano.
In any case, he didn't die in a car accident in downtown Berkeley, as a lot of historical Jesus scholars would have it. It was very purposeful.
But, for the sake of the OP... I imagine that Christianity just would have died out. Indeed, until the resurrection appearances, it
was dying out. True messiahs don't get crucified, and when messianic figures do, their disciples scatter- just like the apostles did, fleeing back to Galilee.
No resurrection, no Christianity. There's no other reason for the movement to continue on after the death of their messiah without a resurrection. It just doesn't make sense.