Fortunately, Christianity will never be proven wrong. It will grow more apparent that it is completely right as the tribulation unfolds. All the things predicted in the book of the Bible Revelation will come to pass.
The second coming is a failed prophecy. First off all the signs of this is going to happen are things that happen all the time. Second of all it was suppose to have already happen.
For example Paul in his first person account states that they would be alive for the second coming. (Using NIV)
1 Thessalonians 4:16-17
For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first.
After that,
we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever.
Another example of how Paul thought the end times were near.
1 Corinthians 7:27-31
Are you married? Do not seek a divorce. Are you unmarried? Do not look for a wife.
But if you do marry, you have not sinned; and if a virgin marries, she has not sinned. But those who marry will face many troubles in this life, and I want to spare you this.
What I mean, brothers, is that the time is short. From now on those who have wives should live as if they had none;
those who mourn, as if they did not; those who are happy, as if they were not; those who buy something, as if it were not theirs to keep;
those who use the things of the world, as if not engrossed in them.
For this world in its present form is passing away.Another example of how this was to pass during Biblical times.
1 John 2:18
Dear children, this is the last hour; and as you have heard that the antichrist is coming, even now many antichrists have come. This is how we know it is the last hour.
Jesus eludes to the second coming during his disciples life time.
Matthew 10:23
When you are persecuted in one place, flee to another. I tell you the truth, you will not finish going through the cities of Israel before the Son of Man comes.
Here Jesus flat out says it will in these guys lifetimes.
Matthew 16:27-28
For the Son of Man is going to come in his Father's glory with his angels, and then he will reward each person according to what he has done.
I tell you the truth, some who are standing here will not taste death before they see the Son of Man coming in his kingdom."
And again Jesus says it flat out that it's in these guys lifetime.
Matthew 24:34
I tell you the truth, this generation will certainly not pass away until all these things have happened.
Repeating in Mark.
Mark 13:30
I tell you the truth, this generation will certainly not pass away until all these things have happened.
And in Luke.
Luke 21:32
"I tell you the truth, this generation will certainly not pass away until all these things have happened.
From Jesus Generation always refers to the people of that particular age. (saying this since some try to get Generation to mean something else.)
There have also been retcons in the Bible to try and create an out for this failed prophecy.
Excavating The Empty Tomb (beyond a reasonable doubt) part 12b