It's a useful exercise to ask religious people what it would take for them to either abandon the "nonnegotiables" of their fath - like the view that Jesus was divine or that the Quran is the world of Allah - or to give-up on their faith entirely.
That's easy and well-known: Were the corpse of Jesus to be discovered, Christianity would be decisively disproven. And it's not so ridiculous as it might sound: We have in fact found the tombs of victims of Roman crucifixion.
Were the tomb of Mary to be discovered, especially with a body in it, that would disprove Roman Catholicism since the Church has taught the Doctrine of the Assumption authoritatively, but it would not necessarily disprove Christianity as such. But I would have a hard time continuing in Christian belief in such an event since my own faith is based on the historical witness of the Church.