If you knew, beyond any reasonable doubt, that God was real. If He appeared to you, in the flesh, said who He was, and you touched Him, talked to Him, heard Him answer your questions about existance, creation, etc. If there was no denying that He was real. If He was as real as your child standing in your living room right now...would it change your mind about Him?
Because knowing He's real vs. believing that He's there to save you, and trusting in HIM for your life decisions... that's totally different. Just because you know for a fact that He's there, doesn't mean you're going to put your trust in Him to take care of you.
Assuming the Bible is truth (humor me if you disagree, here. Just go into this scenario), it says that when God comes back again, EVERY EYE shall see Him. Everyone on earth will know that He's 100% real.
But it also says that not everyone on earth will believe in Him.
I feel like if I saw a celestial being appear in the sky and tell me He's God, and He created the earth, and everything in it, I would have a hard time NOT believing in Him. But apparently, seeing isn't always believing.
You could apply the same thought train to any religion really. If Buddha showed up, and you knew without a doubt that he was Buddha, and his teachings were real, and he truly did find inner peace through the paths laid out in his writings....would you believe in him? Would you label yourself Buddhist after that? If someone could somehow prove to you that their faith was THE faith and it was completely 100% true and not fantastical in any way... would you put your faith in it too?
I just feel like ppl are always looking for proof... but i don't think proof would always change their minds. I think they'd find another reason to doubt. Maybe because they don't KNOW God well enough to trust him, or maybe because they convince themselves it was a dream, or something else. I think if someone proved to me that the Hindi faith was 100% logical, reasonable and all of the ideas in it were 100% true, I still would have a hard time believing in it. Even with all that "proof". So I guess my point is, "proof" isn't the answer. It isn't the key to your belief... there has to be more than just proof. So what else?